题解 | #合法IP#

def checkip(ip):
    if len(ip) == 4:
        for i in range(4):
            if (
                not ip[i].isdigit()
                or (ip[i][0] == "0" and len(ip[i]) > 1)
                or int(ip[i]) < 0
                or int(ip[i]) > 255
            ):
                return False
        return True
    return False


if checkip(input().split(".")):
    print("YES")
else:
    print("NO")