#include <stdio.h>

int main()
{
    int n;
    scanf("%d", &n);
    
    unsigned long long r[64];
    r[0] = 1;
    r[1] = 1;
    for(int i=2; i<=n; i++){
        r[i] = r[i-1] + r[i-2];
    }
    
    printf("%llu\n", r[n]);
    return 0;
}