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

int main(){
  int n;
  cin >> n;
  bool kamo = true;
  long long a[n];
  for(int i = 0; i < n; i++){
    cin >> a[i];
  }
  
  sort(a, a + n);
  for(int i = 1; i < n - 1; i++){
    if(a[i] == a[i - 1] || (a[i] - a[i - 1]) != (a[i + 1] - a[i])) kamo = false;
  }
  
  if(kamo == false) cout << "NO" << endl;
  else cout << "YES" << endl;
  
}