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

if N == 1:
  print('YES')
else:
  tmp = lst[1] - lst[0]
  
  for i in range(len(lst) - 1):
    if tmp == 0 or tmp != lst[i + 1] - lst[i]:
      print('NO')
      break
  else:
    print('YES')