#include <iostream>

using namespace std;

int main()
{
    freopen ("nunta.in", "r", stdin);
    freopen ("nunta.out", "w", stdout);

    int N;
    long long l, ll, c;

    scanf ("%d", &N);

    l = 1, ll = 1, c  = 1;

    for (int i = 2; i <= N; ++i)
    {
        c = l + ll;
        ll = l;
        l = c;
    }

    printf ("%lld", c);

    return 0;
}