题解 | #合法IP#

while True:
    try:
        nums = input().split('.')
        if len(nums) != 4:
            print('NO')
            continue
        count = 0
        for n in nums:
            if not n.isdigit():
                print('NO')
                break
            else:
                if int(n) > 255:
                    print('NO')
                    break
                else:
                    count += 1
        if count == 4:
            print('YES')
    except:
        break