题解 | #合法IP#

ip_list = input().split('.')

def ifValid(ip_list):
    if len(ip_list) != 4:
        print('NO')
        return
    else:
        for ip in ip_list:
            if not ip.isdigit():
                print('NO')
                return
            else:
                if (int(ip) > 0 and ip.startswith('0')) or int(ip) < 0 or int(ip) > 255:
                    print('NO')
                    return
    print('YES')
    return
ifValid(ip_list)