#include <bits/stdc++.h>
using namespace std;

long long dp[55];

int main(){
    int n;
    cin >> n;
    dp[0] = 1;
    for(int i = 0; i < n; i++){
        dp[i + 1] += dp[i];
        dp[i + 2] += dp[i];
    }
    cout << dp[n] << endl;
}