- Does anybody know where Leva Pontryagin is? - Elena Petrovna asked, having looked around the class. The boy gave good hopes in mathematics and had never missed a class without any reason before. - No," the students' confused voices answered, and Leva's roommate, Alyosha, said: - He hasn't walked for two weeks, Elena Petrovna. - Alyosha, you are friends with Leva, aren't you? - his teacher turned to him. - Yes. And I even know where he lives," Alyosha answered Elena Petrovna's next question. - That's very good," smiled the teacher. - Maybe you guys should go see him, huh, guys? After class? - We will go! - Alyosha answered for everyone, and the rest of the students agreed with him in silence. After the lessons, a few guys and Alyosha went to the house where Leva Pontryagin lived. Like many people at the time, he didn't have a phone in his house, so nobody knew what had happened to him that he started skipping classes. Knocking was the first thing Alyosha decided to do. Levina's mothe