#include <bits/stdc++.h>
using namespace std;

int f(int n) {
    if (n <= 0) return 0;
    if (n == 1) return 1;
    
    int a = 0, b = 1, c;
    for (int i = 2; i <= n; ++i) {
        c = a + b;
        a = b;
        b = c;
    }
    return b;
}

int main() {
    int n;
    cin >> n;
    cout << f(n);
    return 0;
}