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#include <bits/stdc++.h>
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using namespace std;
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long long fib(int n) {
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    if (n <= 1) {
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        return n;
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    }
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    long long f[n + 1];
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    f[0] = 0;
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    f[1] = 1;
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    for (int i = 2; i <= n; ++i) {
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        f[i] = f[i - 1] + f[i - 2];
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    }
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    return f[n];
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}
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int main() {
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    int n;
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    cin >> n;
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    cout << fib(n);
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    return 0;
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}
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