#include <bits/stdc++.h>
using namespace std;
#define REP(i,n) for(int i=0; i<(n); i++)
using LL=long long;
int main()
{
	LL N;
	cin >> N;

	vector<LL> vc(N);
	for( auto &x : vc )
	{
		cin >> x;
	}

	sort( begin( vc ), end( vc ) );

	if( set<LL>( begin( vc ), end( vc ) ).size() != 1 )
	{
		vector<LL> res;
		adjacent_difference( begin( vc ), end( vc ), back_inserter( res ) );
		res.erase( res.begin() );

		if( set<LL>( begin( res ), end( res ) ).size() == 1 )
		{
			cout << "YES" << endl;
			return 0;
		}
	}
	cout << "NO" << endl;

	return 0;
}