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

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

	std::vector<long long> v(n + 2, 1);
	
	for (int i = 2; i <= n; i++) {
		v[i] = v[i - 1] + v[i - 2];
	}

	std::cout << v[n] << std::endl;
	return 0;
}