Walking on a rainy evening without an umbrella, you didn’t even suspect that the next day you would get so sick that you couldn’t get out of bed. Several hours passed, you were getting worse, and you decided to call your friend Derek to help you. After a few seconds, he accepted the call, listening to you. «Okay...I'll be there in twenty minutes.» - he said at the end of the dialogue and hung up. You were just lying on the sofa, covered with a warm blanket, waiting for his arrival, and as he said, twenty minutes later there was a knock on your door, and Derek entered the corridor. «Hey little one, how are you feeling?»