#!/usr/bin/env python
#coding:UTF-8

N = int(raw_input())
x1 = map(int,raw_input().split())

x2 = sorted(x1)
calc = x2[1] - x2[0]
judge = "YES"

for I in range(2,N):
     calc2 = x2[I] - x2[I - 1]
     if calc2 == 0 or calc != calc2:
          judge = "NO"

print judge