题解 | #合法IP#

while 1:
    try:
        ip = input().split('.')

        counter = 0

        if len(ip) != 4:
            print('NO')
            break
        else:
            for i in range(4):
                if not ip[i].isdigit():
                    print('NO')
                    break
                elif int(ip[i]) > 255 or int(ip[i]) <0 or (len(ip[i]) > 1 and ip[i][0] == '0'):
                    print('NO')
                    break
                counter += 1
            if counter == 4:
                print('YES')
    except:
        break