#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#include <iostream>
#include <map>
#include <set>
#include <list>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <queue>
#include <iomanip>

#define ll long long
#define SIZE 10001

using namespace std;

/* フィボナッチ数列 */
ll fibo(int n)
{
	ll a = 0;
	ll b = 1;
	ll res;
	int i;

	if (n == 0 || n == 1) return (n);
	for (i = 2; i <= n; i++) {
		res = a + b;
		a = b;
		b = res;
	}
	return (res);
}

int main()
{
	int N;

	cin >> N;

	cout << fibo(N + 1) << endl;
}