def login_system():
    import csv
    while_loop = True
    with open('Usernames and Passwords.csv', 'rt') as csv_file:
        username_password = csv.DictReader(csv_file)
        for row in username_password:
            while while_loop is True:
                username = input("Username:").lower()
                if username != row['Username']:
                    print("Declined")
                else:
                    print("Accepted")
                    password = input("Password:").lower()

                    if password != row['Password']:
                        print("Invalid Password")
                        login_system()
                    else:
                        print("Welcome", row['Name'].title())
                        while_loop = False


login_system()