#include <iostream>
#include <iomanip>
#include <cmath>
#include <algorithm>

typedef long long ll;

int main(void)
{
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  std::cout << std::fixed << std::setprecision(13);
  int n;
  std::cin >> n;
  ll x[n];
  for (int i = 0; i < n; ++i) std::cin >> x[i];
  std::sort(x, x+n);
  ll diff = x[1] - x[0];
  if (diff==0) {std::cout << "NO" << std::endl; return 0;}
  for (int i = 2; i < n; ++i) {
    if (x[i] - x[i-1] != diff) {std::cout << "NO" << std::endl; return 0;}
  }
  std::cout << "YES" << std::endl;
  return 0;
}