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

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