#include<iostream>
#include<stdio.h>
#include<stdlib.h>
#include<algorithm>
#include<vector>
#include<string.h>
#include<math.h>
#include<map>
#include<iomanip>
#include<queue>

using ll = long long;

using namespace std;

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