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#include<bits/stdc++.h>
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using namespace std;
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typedef long long ll;
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#define sz(s) (int)(s).size()
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#define all(s) s.begin(),s.end()
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void Speed() {
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    ios_base::sync_with_stdio(false);
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    cin.tie(NULL);
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}
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struct suffix_automaton {
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    static const int alpha = 26, offset = 'a';
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    struct state {
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        int len = 0, link = 0, cnt = 0;
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        int next[alpha];
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        state(int len = 0) : len(len) {
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            memset(next, -1, sizeof(next));
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        }
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        state(int len, const state& other) : len(len) {
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            link = other.link;
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            for(int i = 0; i < alpha; i++) {
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                next[i] = other.next[i];
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            }
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        }
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    };
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    vector<state> st;
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    vector<ll> dp;
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    int last = 0;
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    suffix_automaton() {
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        st.push_back(state());
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        st[0].link = -1;
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    }
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    suffix_automaton(const string &s) : suffix_automaton() {
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        for (char ch : s) extend(ch - offset);
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        dp = vector<ll>(sz(st), -1);
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        calc_number_of_occurrences();
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    }
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    void extend(int c) {
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        int cur = sz(st), p = last;
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        st.push_back(state(st[last].len + 1));
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        st[cur].cnt = 1;
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        for(; ~p && st[p].next[c] == -1; p = st[p].link) {
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            st[p].next[c] = cur;
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        }
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        if(p == -1) {
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            st[cur].link = 0;
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        } else {
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            int q = st[p].next[c];
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            if(st[p].len + 1 == st[q].len) {
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                st[cur].link = q;
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            } else {
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                int clone = sz(st);
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                st.push_back(state(st[p].len + 1, st[q]));
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                for(; ~p && st[p].next[c] == q; p = st[p].link) {
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                    st[p].next[c] = clone;
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                }
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                st[q].link = st[cur].link = clone;
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            }
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        }
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        last = cur;
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    }
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    void calc_number_of_occurrences() {
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        vector<pair<int, int>> v;
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        for (int i = 1; i < sz(st); i++)
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            v.emplace_back(st[i].len, i);
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        sort(v.begin(), v.end(), greater<>());
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        for (int i = 0; i < sz(st) - 1; i++) {
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            int suf = st[v[i].second].link;
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            st[suf].cnt += st[v[i].second].cnt;
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        }
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    }
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    ll num_different_substrings() {
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        ll ans = 0;
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        for(int i = 1; i < sz(st); i++) {
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            ans += st[i].len - st[st[i].link].len;
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        }
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        return ans;
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    }
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    ll rec(int i) {
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        auto& ret = dp[i];
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        if(~ret) return ret;
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        ret = (i == 0 ? 0 : st[i].cnt);
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        for(int j = 0; j < alpha; j++) {
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            if(~st[i].next[j]) {
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                ret += rec(st[i].next[j]);
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            }
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        }
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        return ret;
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    }
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    string kth_substring(ll k) { // repeated
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        assert(k <= rec(0));
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        string ans;
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        int cur = 0;
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        while(k > 0) {
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            for(int c = 0; c < 26; c++) {
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                if(st[cur].next[c] == -1) continue;
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                int j = st[cur].next[c];
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                if(dp[j] >= k) {
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                    ans += (char)(c + offset); cur = j;
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                    k -= st[j].cnt;
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                    break;
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                }
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                k -= dp[j];
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            }
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        }
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        return ans;
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    }
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};
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void solve() {
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    string s; cin >> s;
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    suffix_automaton sa(s);
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    ll k; cin >> k;
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    if(k > 1ll * sz(s) * (sz(s) + 1) / 2) cout << "No such line.\n";
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    else cout << sa.kth_substring(k) << '\n';
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}
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int main() {
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    Speed();
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    int tc = 1;
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    //cin >> tc;
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    while (tc--) {
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        solve();
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    }
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    return 0;
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}