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

signed main(){
  int N; cin >> N;
  vector< int > X( N );
  for( int i = 0; i < N; ++i )
    cin >> X[ i ];
  sort( X.begin(), X.end() );
  int d = X[ 1 ] - X[ 0 ];
  if( d == 0 )
    cout << "NO" << endl,
    exit( 0 );
  for( int i = 1; i < X.size(); ++i )
    if( X[ i ] - X[ i - 1 ] != d )
      cout << "NO" << endl, 
      exit( 0 );
  cout << "YES" << endl;
  return 0;
}