#include <iostream>

using namespace std;

int f(int n) {
    if (n == 0)return 0;
    else if (n == 1)return 1;
    return f(n - 1) + f(n - 2);
}
int main() {
    int n;
    cin >> n;
    cout << f(n) << endl;
    return 0;
}