#include<iostream>
using namespace std;
long long int dp[52] = { 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;
	return 0;
}