#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
using namespace std;

#define ll long long
#define INF (1 << 30)
#define INFLL (1LL << 60)

int n;
ll memo[100];

ll saiki(int now){
	if(now > n) return 0;
	if(memo[now] != INFLL) return memo[now];
	if(now == n) return 1;
	ll sum = 0;
	for(int i = 1;i <= 2;i++){
		sum += saiki(now + i);
	}
	return memo[now] = sum;
}

int main() {
	for(int i = 0;i < 100;i++){
		memo[i] = INFLL;
	}
	cin >> n;
	ll ans = saiki(0);
	cout << ans << endl;
	return 0;
}