//No.406 鴨等間隔の法則

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

namespace
{
int X[ 100010 ];
}

int main()
{
int i;
int N;
int iDiff;

	cin >> N;
	for( i = 0; i < N; i++ ) cin >> X[ i ];

	sort( X, X + N );

	iDiff = X[ 1 ] - X[ 0 ];
	if( iDiff == 0 )
	{
		cout << "NO" << endl;

		return 0;
	}

	for( i = 2; i < N; i++ )
	{
		if( X[ i ] - X[ i - 1 ] != iDiff )
		{
			cout << "NO" << endl;

			return 0;
		}
	}

	cout << "YES" << endl;

	return 0;
}