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

ll memo[55];

ll f(int n){
  if(memo[n]) return memo[n];
  memo[n] = 1;
  if(n < 2) return memo[n] = 1;
  else return memo[n] = f(n-1)+f(n-2);
}

int main(){
  int n; cin >> n;
  cout << f(n) << endl;
  return 0;
}