/* -*- coding: utf-8 -*-
 *
 * 786.cc:  No.786 京都大学の過去問 - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 50;

/* typedef */

typedef long long ll;

/* global variables */

ll dp[MAX_N + 1];

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d", &n);

  dp[0] = 1;
  for (int i = 0; i < n; i++) {
    dp[i + 1] += dp[i];
    if (i + 1 < n) dp[i + 2] += dp[i];
  }

  printf("%lld\n", dp[n]);
  return 0;
}