users = {

    'amir' : '1376',

    'reza' : '1380',

    'pedram' : '1375'

}

entered_username = input('Enter your username: ')

while entered_username in users:

   break

else:

    print('Username is invalid')

     entered_username = input('Try another username: ')

entered_password = input('Enter your password: ')

while users[entered_username] != entered_password:

    print('Password is invalid')

    entered_password = input('Try another password: ')

    print('You have loged in successfully')