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

int main(void){
	int N; cin >> N;
	long long dp[51];
	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;
}