题解 | #合法IP#

import re
def checkip(ipl):
    if len(ipl)!=4:
        print('NO')
        return
    for i in ipl:
        if len(i)>1 and i.startswith('0'):
            print('NO')
            return
        elif not re.search('[0-9]',i[0]):
            print('NO')
            return
        i = int(i)
        if i < 0 or i > 255:
            print('NO')
            return
    else:
        return True

try:
    ipl = input().split('.')
    if checkip(ipl):
        print('YES')    
except:
    print('NO')