摘要：
Consider equations having the following form: a*x1^2+b*x2^2+c*x3^2+d*x4^2=0 a, b, c, d are integers from the interval [-50,50] and any of them cannot 阅读全文
摘要：
Ignatius is so lucky that he met a Martian yesterday. But he didn't know the language the Martians use. The Martian gives him a history book of Mars a 阅读全文
摘要：
Misha hacked the Codeforces site. Then he decided to let all the users change their handles. A user can now change his handle any number of times. But 阅读全文