//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(){
  int N; cin >> N;
  vector<int> X(N);
  for(int i = 0; i < N; i++) cin >> X[i];
  
  sort(X.begin(), X.end());
  
  for(int i = 1; i < N-1; i++){
    if(X[i-1] == X[i] or X[i] == X[i+1]){
      printl("NO");
      return 0;
    }
    
    if(X[i]-X[i-1] != X[i+1]-X[i]){
      printl("NO");
      return 0;
    }
  }
  
  printl("YES");
  return 0;
}