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

int main() {
	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 - 2] + dp[i - 1];
	}
	cout << dp[n] << endl;

	return 0;
}