#include <iostream>
#include <algorithm>
using namespace std;
int x[100005];
int main(void) {
  int N;
  cin.tie(0);

  cin >> N;
  for(int i = 0;i < N; i++) cin >> x[i];
  sort(x, x+N);
  int dif = x[1] - x[0];
  for (int i = 1; i < N-1; i++) {
    if(dif != x[i+1]-x[i]) {
      dif = 0;
      break;
    }
  }

  if(dif) cout << "YES\n";
  else cout << "NO\n";
  return 0;
}