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

long long 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;
}