Vitya and Masha are playing a game. At first, Vitya thinks of three different integers. In one move Masha can ask one of the following three numbers: the sum of the numbers, the product of the numbers or the sum of pairwise products of the numbers. Masha asks questions and Vitya immediately answers before Masha asks the next question. a) Prove that Masha can always guess Vitya's numbers. b) What is the least amount of questions Masha needs to ask to guaranteely guess them?