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

if kamo_list[0] == 0:
    diff = kamo_list[1]
    start_index = 2
else:
    diff = kamo_list[0]
    start_index = 1

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

print(equal_interval)