#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstring>
#include <cmath>
#include <vector>
#include <list>
#include <string>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <functional>
using namespace std;
typedef long long int llint;
const int INF = 1000000;
const llint LINF = 100000000;
//何番目
int black[10000] = { 0 }, bn, wn;
int white[10000] = { 0 };
llint dp[INF];
int main() {
	dp[0] = 1;
	int n;
	cin >> n;
	for (int i = 0; i <= n; i++) {
		dp[i + 1] += dp[i];
		dp[i + 2] += dp[i];
	}
	cout << dp[n];
	
	return 0;
	
}