摘要：
D. Friendly Spiders Mars is home to an unusual species of spiders — Binary spiders. Right now, Martian scientists are observing a colony of $n$ spider 阅读全文
摘要：
C. Interesting Sequence Petya and his friend, robot Petya++, like to solve exciting math problems. One day Petya++ came up with the numbers $n$ and $x 阅读全文