Day1：编写登入接口

输入用户名密码；

登入成功后提示欢迎信息；

三次登入失败后锁定。

编写如下：

# Author: Ewan Wang
for i in range(3):
   username = input("username:")
   password = input("password:")
   if username =="Wang"and password =="123":
     print("Welcome to the new world!")
     break
   else:
     print("Username or password is wrong,please re-enter...")
else:
    print("The system has been locked.")