Ural 1323 Classmates源码，递归、DFS-Descr iption

Tanya almost left for school when the telephone rang. It was the director of studies. She said the first three lessons that day had been cancelled because of an electricity failure. Tanya was the head girl of the class and the director of studies asked her to pass this news to her classmates.

— What shall I do? — thought Tanya, — there is almost no time! OK, now I’m going to call Lena, then Katya, then Masha. Lena will meantime call Vitya, she knows his telephone number, Vitya will call Masha. No, I’ll call Masha myself: let him better call Misha. Katya will call Natasha... No, it won’t work. They quarreled yesterday. Thus there is no time to think. I must immediately call Lena. Hit-or-miss everyone will know the news.

Tanya managed to send this message to all her classmates. But someone knew it very late and someone heard this news　several people. In the evening, Tanya decided to work out a plan of calls and not to let it ride the next time. After all, she is the head