function os()
loggedin = "no"

user1 = "mad1231999"
pass1 = "helloworld"

    shell.run("clear")
    write("MadOS 0.1 by Mads Clausen\n> ")
    cmd = read()

    if cmd == "login" then

        if loggedin == "yes" then

            write("\nYou are already logged in,\ntype 'logout' to log out")
            sleep(3)
            os()

        else

            shell.run("clear")
            print("")
            print("")
            print("")
            print("       Login: Enter username and password")
            print("")
            write("       Username: ")
            user = read()

            shell.run("clear")
            print("")
            print("")
            print("")
            print("       Login: Enter username and password")
            print("")
            write("       Password: ")
            pass = read("*")

            if user == user1 and pass == pass1 then

                loggedin = "yes"
                os()

            end

            if (user == user1 and pass ~= pass1) or (user ~= user1 and pass == pass1) then

                print("\n       Login failed")
                sleep(2)
                os()

            end

        end

    end

end

os()