#include <iostream>
#include <random>
// #include <algorithm>
#define INF 1000000000
using namespace std;
#define int long long



signed main(){
  int N;
  int D[52]={1,1,1};
  cin >> N;
  if(N<=2){
    cout << D[N] << endl;
    return 0;
  }
  for(int i=2;i<=N;i++){
    D[i]=D[i-1]+D[i-2];
  }
  cout << D[N] << endl;
}