#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;


int main(){
  int N;
  cin >> N;
  vector<ll> dp(55, 0);
  dp[0] = 1;

  rep(i,N){
    dp[i+1] += dp[i];
    dp[i+2] += dp[i];
  }

  cout << dp[N] << endl;
  
  return 0;
}