#include <bits/stdc++.h>
using namespace std;

#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define repi(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define all(x) (x).begin(),(x).end()
#define foreach(u,v) for(auto (u) : (v))
#define pb push_back
#define mp make_pair
#define mt make_tuple

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<ll, ll> pll;
typedef vector<ll> vl;

const int inf = 1e9;
const ll linf = 1LL<<60;
const ll mod = 1e9 + 7;
const double eps = 1e-9;

/*
dp[i][j]
 i段目までの場合の数
 j = 1のとき2段とび
*/

int n;
ll dp[51];

int main()
{
  cin >> n;

  dp[0] = 1;
  rep(i, n){
    dp[i+1] += dp[i];
    if(i+2 <= n) dp[i+2] += dp[i];
//    cout << i << ":" << dp[i][0] << " " << dp[i][1] << endl;
  }

  cout << dp[n] << endl;

  return 0;
}