#include <iostream>
#include <vector>
using namespace std;
int main(void) {
	int n;
	cin >> n;
	vector<long long> dp(100, 0);
	dp[1] = 1, dp[2] = 2;
	for (int i = 3; i < 100; ++i) {
		dp[i] = dp[i - 1] + dp[i - 2];
	}
	cout << dp[n] << endl;
	return 0;
}