#include <iostream>

using namespace std;

const int MAXN = 50;

int N;
long long dp[MAXN + 2];

int main() {
	cin >> N;
	dp[0] = 1;
	for (int i = 0; i < N; i++) {
		dp[i + 1] += dp[i];
		dp[i + 2] += dp[i];
	}
	cout << dp[N] << endl;
	return 0;
}