#include <bits/stdc++.h>
using namespace std;
using ll = long long;

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