题解 | #合法IP#

import sys

lst = input().split('.')
for i in lst:
    if len(i)>1 and i[0] not in '123456789':
        print('NO')
        sys.exit()
try:
    lst = list(map(int, lst))
except:
    print('NO')
    sys.exit()

if len(lst) != 4:
    print('NO')
    sys.exit()
for i in lst:
    if i < 0 or i > 255:
        print('NO')
        break
else:
    print('YES')