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#include <bits/stdc++.h>
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#define ll long long
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using namespace std;
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ll dp[51];
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bool calced[51];
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ll calc(int n) {
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    if (n < 0) {
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        return 0;
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    } else if (n == 0) {
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        return 1;
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    } else if (calced[n]) {
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        return dp[n];
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    } else {
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        dp[n] = calc(n - 1) + calc(n - 2) + calc(n - 3);
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        calced[n] = true;
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        return dp[n];
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    }
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}
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int main() {
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    std::ios_base::sync_with_stdio(false);
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    cin.tie(0);
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    cout.tie(0);
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    int n;
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    cin >> n;
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    cout << calc(n);
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    return 0;
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}