//Normal

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

void print(auto a){
  cout << a;
}

void prints(auto a){
  cout << a << " ";
}

void prints(){
  cout << " ";
}

void printl(auto a){
  cout << a << endl;
}

void printl(){
  cout << endl;
}

void fix(int n){
  cout << fixed << setprecision(n);
}

int main(){
  vector<ll> dp(100, 1);
  for(int i = 2; i <= 50; i++){
    dp[i] = dp[i-2]+dp[i-1];
  }

  int N; cin >> N;

  printl(dp[N]);

  return 0;
}