The technologies are rapidly evolving - only 50 years ago a simple black-and-white TV was a luxury! And now even a cool big color TV with remote control is a common thing. Let's try to improve our TV and add the voice control to it! To begin with, we’ll write the simple prototype in Python. It’ll use the following commands:

first_channel() - turns on the first channel from the list.
last_channel() - turns on the last channel from the list.
turn_channel(N) - turns on the N channel. Pay attention that the channel numbers start from 1, not from 0.
next_channel() - turns on the next channel. If the current channel is the last one, turns on the first channel.
previous_channel() - turns on the previous channel. If the current channel is the first one, turns on the last channel.
current_channel() - returns the name of the current channel.
is_exist(N/'name') - gets 1 argument - the number N or the string 'name' and returns "Yes", if the channel N or 'name' exists in the list, or "No" - in the other case.

The default channel turned on before all commands is №1.
Your task is to create the VoiceCommand class and methods described above.
In this mission you could use the Iterator design pattern.

Example:

CHANNELS = ["BBC",...