n = input()
kamo_list = sorted(list(map(int, input().split(' '))))



equal_interval = 'YES'
diff = kamo_list[1] - kamo_list[0]
if diff == 0:
    equal_interval = 'NO'
for i in range(2,len(kamo_list)):
    if kamo_list[i] - kamo_list[i-1] != diff:
        equal_interval = 'NO'

print(equal_interval)