N = int(input().strip())
x = sorted([int(i) for i in input().strip().split(' ')])

lst = [(b - a) for a, b in zip(x, x[1:]) if b - a != 0]

if len(lst) != N - 1:
  print('NO')
  exit(0)

lst = list(set(lst))
print(['YES', 'NO'][len(lst) != 1])