题解 | #合法IP#

ip = input().strip().split('.')

if len(ip) != 4:
    print("NO")
else:
    is_legal = True
    for i in ip:
        if not i.isnumeric():
            is_legal = False
            break
        elif len(i) > 3:
            is_legal = False
            break
        elif len(i) > 1 and i[0] == '0':
            is_legal = False
            break
        elif int(i) < 0 or int(i) > 255:
            is_legal = False
            break
    if is_legal:
        print("YES")
    else:
        print("NO")