At the first glance,this problem is hard to understand what it says and seem to be difficult.After thinking for a while,you'll find it can be done in a very easy way.(Email:hyz12345678@163.com)

Re: At the first glance,this problem is hard to understand what it says and seem to be difficult.After thinking for a while,you'll find it can be done in a very easy way.(Email:hyz12345678@163.com)