#include <iostream>
#include <cstdio>
#include <string>
#include <algorithm>

using namespace std;

int n;

int res (int n) {
    if(n == 0) return 0;
    else if (n == 1) return 1;
    else return res(n - 1) + res(n - 2);
}

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