#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
//#define int long long
using namespace std;

int N;
int x[100000];

signed main()
{
	cin >> N;
	rep(i,N) cin >> x[i];
	sort(x, x + N);

	//rep(i,N) cout << x[i] << endl;

	if (x[1] == x[0])
	{
		cout << "NO" << endl;
		return 0;
	}
	int sa = x[1] - x[0];
	for (int i=1; i<=N-2; i++)
	{
		if (x[i+1] == x[i])
		{
			cout << "NO" << endl;
			return 0;
		}
		if (x[i+1] - x[i] != sa)
		{
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;
}