“register username password”: to register a new user with name “username” and password “password”. If such user already exists in the database, the system should output the error message “fail: user already exists”. Otherwise, it should output message “success: new user added”.“login username password”: to log into the system as user “username” with password “password”. If such user does not exist, the system should output “fail: no such user”. Otherwise, if the user enters an incorrect password, the system should output “fail: incorrect password”. Otherwise, if the user is already logged in the system at that moment, it should output “fail: already logged in”. Otherwise, it should output “success: user logged in”.“logout username”: to log out of the system as user “username”. If such user does not exist, the system should output “fail: no such user”. Otherwise, if the user isn’t in the system at that moment, it should output “fail: already logged out”. Otherwise, it should output “success: user logged out”.
，找回自我，歇够了，再飞回来，继续面对自己的人生。
