#include <iostream>
using namespace std;

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

	static long long dp[100];
	dp[0] = 1;

	for (int i = 0; i <= 50; i++) {
		dp[i + 1] += dp[i];
		dp[i + 2] += dp[i];
	}

	cout << dp[n] << endl;

	return 0;
}