#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main(void){
  int n;
  cin >> n;
  long long x[n];
  for(int i = 0; i < n; i++) cin >> x[i];
  sort(x, x + n);
  long long d = x[1] - x[0];
  if(d == 0){
    cout << "NO" << endl;
    return 0;
  }
  for(int i = 1; i < n - 1; i++){
    if(x[i + 1] - x[i] != d){
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
  return 0;
}