#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
signed main() {
	ios::sync_with_stdio(false); cin.tie(0);
	int n;
	cin >> n;
	vector<long long> dp(n + 2);
	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;	
}