#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>

using namespace std;

int main() {
	int n;

	cin >> n;
	vector<long long> dp(n + 1 + 2, 0);
	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;
}