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

long long int dp[55];
int main(){
    int n; 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;
}