#include <iostream>
using namespace std;


int main() {
	int n;
	cin >> n;

	long long dp[55] = { 1, 1 };

	for (int i = 2; i < 55; i++) {
		dp[i] = dp[i - 2] + dp[i - 1];
	}

	cout << dp[n] << endl;

	return 0;
}