I got an idea of this problem.
First we reverse this string, then we use dp to find the LCS of these two strings. Using dp will take O(2n) space, but will use O(n^2) time. TLE! Is there anybody to help me? Thanks!

My friend Avench, is a very funny person. He is very heavy and beautiful. In our team, he is welcomed. 
 We all love to play tricks on him. For instance, sometimes we ask him what his last name is. And he always becomes shy and tell us that his last name is "A'le'ni". So we call him "A'le'ni Wencheng".
 Because of his first name "Wencheng", we connect him with the Princess Wencheng in Tang Dynasty. And I posted a problem on "218.77.114.14:8080" Online Judge called "Princess WenCheng married the king of Tibet". You can try to solve it although it is very, very simple.
 In codeforces, his ID is "***". He loves beautiful girls. If you want to contact him, please tell me and I am glad to help you to tell him!!!

It's my first time to take part in the contest. It was so fun. The problem 4 has been hacked by someone, that was a pity.

 Neither data structure nor algorithm that I have used, I'm just a green hand.