#include <iostream>
#include <cstring>

using namespace std;

const int N = 20;

int dp[N];

int main(){
    int n;
    cin >> n;
    memset(dp, 0, sizeof(dp));
    dp[0] = 1;
    dp[1] = 1;
    dp[2] = 2;
    for(int i = 3; i <= n; i++){
        dp[i] = dp[i-1] + dp[i-2];
    }
    printf("%d\n", dp[n]);
    return 0;
}