#include <iostream>
#include <vector>
using namespace std;

int main() {
	int N;
	cin >> N;
	vector<long> fibonacci{ 1, 1, 2 };
	for (int i = 3; i < N + 1; ++i) {
		for (size_t j = 0; j < 2; ++j) fibonacci.at(j) = fibonacci.at(j + 1);
		fibonacci.at(2) = fibonacci.at(0) + fibonacci.at(1);
	}
	if (N == 1) cout << fibonacci.at(1);
	else cout << fibonacci.at(2);
}