#include<iostream>
using namespace std;
int main(){
    int N;
    long long dp[51];
    cin >> N;
    dp[0] = 1;
    dp[1] = 1;
    for(int i=2;i<=N;i++){
        dp[i] = dp[i-1]+dp[i-2];
    }
    cout << dp[N] << endl;
    return 0;
}