n = int(input())
li = list(map(int, input().split()))

li.sort()
dif = li[1] - li[0]

def judge(li, dif):

    for i in range(n - 1):
        if dif == 0 or not li[i + 1] - li[i] == dif:
            return('NO')
    return 'YES'

print(judge(li, dif))