#include "bits/stdc++.h"

using namespace std;
typedef long long ll;
const ll MOD = 1e9 + 7;
ll dp[51];
int main() {
	int N;
	cin >> N;
	dp[0] = 1;
	for (int i = 0; i < N; i++) {
		dp[i + 1] += dp[i];
		if (i + 2 <= N) dp[i + 2] += dp[i];
	}
	cout << dp[N] << endl;
}