#include <iostream>

using namespace std;

int dfs(int n)
{
    if(n == 1) return 1;
    if(n == 2) return 2;

    return dfs(n - 1) + dfs(n - 2);
}

int main ()
{
    int n;
    cin >> n;

    cout << dfs(n);

    return 0;
}