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

int main()
{
	int N;
	cin >> N;
	vector<long long> x( N );
	for( int i = 0; i < N; i++ ) {
		cin >> x[i];
	}

	sort( x.begin(), x.end() );
	string ans = "YES";
	long long last = x[0];
	long long d = -1;
	for( int i = 1; i < N; i++ ) {
		if( d >= 0 && x[i] - last != d || last == x[i] ) ans = "NO";
		d = x[i] - last;
		last = x[i];
	}

	cout << ans << endl;
}