/* -*- coding: utf-8 -*-
 *
 * 406.cc: 
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 100000;

/* typedef */

/* global variables */

int as[MAX_N];

/* subroutines */

/* main */

int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) cin >> as[i];
  sort(as, as + n);

  int d = as[1] - as[0];
  bool ok = (d > 0);
  for (int i = 1; ok && i < n - 1; i++)
    ok = (d == as[i + 1] - as[i]);

  cout << (ok ? "YES" : "NO") << endl;
  return 0;
}