#define _GLIBCXX_DEBUG
#define ll long long
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

int main(){
  int N; cin >> N;
  vector<ll> A(55, 0);
  A[0] = 1, A[1] = 1;
  for(int i = 2; i <= N; i++){
    A[i] = A[i-2] + A[i-1];
  }
  cout << A[N] << endl;
}