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