#include <bits/stdc++.h>
using namespace std;

int n;
long long dp[60];

int main()
{
	cin >> n;
	dp[0] = 1;
	for (int i = 0; i < 50; i++){
		dp[i + 1] += dp[i];
		dp[i + 2] += dp[i];
	}
	cout << dp[n] << endl;
}