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

signed main() {
  int N;
  cin >> N;

  vector<int> A(N);
  for( int i = 0; i < N; i++ ) cin >> A.at(i);
  sort(A.begin(), A.end());

  int sa;
  for( int i = 1; i < N; i++ ){
    if( i == 1 ) sa = A.at(i)-A.at(i-1);
    else{
      if( A.at(i) - A.at(i-1) != sa ){
        cout << "NO" << endl;
        return 0;
      }
    }
    if( A.at(i) == A.at(i-1) ){
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
}