题解 | #合法IP#

import sys

for line in sys.stdin:
    a = line.strip()
    try:
        a1 = list(a.split("."))
        if len(a1) != 4:
            print("NO")
        else:
            for i in a1:
                if int(i) not in range(256):
                    print("NO")
                    break
                elif len(str(int(i))) != len(i):
                    print("NO")
                    break                 
            else:
                print("YES")
    except:
        print("NO")