import strutils, sequtils, algorithm

var
  N, x = readLine(stdin).split.map parseInt
  yes = true

x.sort(cmp)
let diff = x[1] - x[0]

if diff != 0:
  for i in 1 ..< x.high:
    if diff != x[i + 1] - x[i]:
      yes = false
      break
else:
  yes = false

["NO", "YES"][int(yes)].echo