#include <stdio.h>

int n;
long long m[110] = {1, 1, 2, };
int main()
{
    freopen(".10.in","r",stdin);
    freopen(".10.out","w",stdout);
    scanf("%d", &n);
    for(int i = 3 ; i <= n ; i++ )
        m[i] = m[i-1] + m[i-2];
    printf("%lld", m[n]);
}