#include <iostream>
#include <cstdlib>

int main()
{
    int n;
    std::cin >> n;
    long long a[51];
    a[0] = 1; a[1] = 1;
    for(int i = 2; i <= n; i++){
        a[i] = a[i - 1] + a[i - 2];
    }
    std::cout << a[n] << std::endl;
}