def d():
  if len(set(x))!=n:return "NO"
  s=set()
  a=x.pop()
  while x:
    b=x.pop()
    s.add(a-b)
    a=b
  return ("NO","YES")[len(s)==1]

n=int(input())
x=sorted([i for i in map(int,input().split())])
print(d())