N = int(input())
x = [int(i) for i in input().split()]
x.sort()
s = x[1] - x[0]
flag = True
for i in range(N - 1):
	if x[i + 1] == x[i] or x[i + 1] - x[i] != s:
		flag = False
		break
if flag:
	print("YES")
else:
	print("NO")