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

const int N = 25;
int n, f[N];

int main()
{
    f[0] = f[1] = 1;

    cin >> n;
    for(int i = 2; i <= n; i ++)
    {
        f[i] = f[i - 1] + f[i - 2];
    }

    cout << f[n] << endl;

    return 0;
}