He goes to the post office and tries to call Katya Snegireva on her memorable phone number 50-50-2, or as he says himself, "rug-rug or two." The answer comes back - Katya has left.
He goes to the post office and attempts to contact Katya Snegireva using her memorable phone number, 50-50-2, which is described as a distinctive identifier for her. The call results in an unsuccessful connection because Katya has left.