#include <iostream>
using namespace std;

long dp[55];

int main(){
    int n;
    cin >> n;

    dp[0] = dp[1] = 1;
    for(int i = 2; i <= n; i++){
        dp[i] = dp[i - 1] + dp[i - 2]; 
    }

    cout << dp[n] << endl;
}