#include <iostream>
using namespace std;

int main() {
	long long int dp[55];
	int n,i;
		cin >> n;
		dp[0]=dp[1] =1;
		for (i = 2; i <= n; i++) {
			dp[i] = dp[i - 1] + dp[i-2];
		}
		cout << dp[n];
		return 0;
}