#encoding: utf-8

ans = "YES"
n = input()
duck = []

for i in range(0, n):
    duck.append(input())

duck.sort()

a = duck[1] - duck[0]

for i in range(0, n):
    if (duck[i] - duck[i-1]) != a or duck[i] == duck[i-1]:
        ans = "NO"
        break

print ans