#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
	int n;
	cin >> n;

	vector<unsigned long long> dp(n + 1, 0);
	dp[0] = 1;
	dp[1] = 1;
	for(auto i = 2; i <= n; ++i) {
		dp[i] = dp[i - 1] + dp[i - 2];
	}

	cout << dp[n] << endl;
}