username = "python"
userpassword = "123456"
while True:
    name = input("请输入用户名:")
    password = input("请输入密码:")
    if name == username and password == userpassword:
        print("登录成功!")
        break
    if name!=username:
        print("用户名不存在，请重新输入!")
        continue
    if password !=userpassword:
        print("密码输入有误，请重新输入！")    
print("欢迎来到贝尔编程!")