n = int(input())
x = [int(x) for x in input().split()]
x.sort()
sp = x[1] - x[0]
res = True
for i in range(len(x) - 1):
  d = x[i + 1] - x[i]
  if d == 0 or d != sp:
    res = False
    break
if res:
  print('YES')
else:
  print('NO')