Fib

#include <iostream>

using namespace std;

int main()
{
    int f1 = 0, f2 = 1, f3;
    int n;
    cin >> n;
    for (int i = 1; i < n; ++i) {
        f3 = f2+f1;
        f1 = f2;
        f2 = f3;
    }

    cout << f3 << endl;

    return 0;
}