func main()
	var ss: [][]char
	var n: int :: cui@input().toInt(&)
	do ss :: cui@input().split(" ")
	var a: []int :: #[n]int
	for i(0, n - 1)
		do a[i] :: ss[i].toInt(&)
	end for
	do a.sort()
	
	var ans: bool :: a[0] <> a[1]
	for i(1, n - 1)
		if(a[i] - a[i - 1] <> a[1] - a[0])
			do ans :: false
		end if
	end for
	do cui@print(ans ?("YES\n", "NO\n"))
end func