IOIPALIN  Palindrome 2000
A palindrome is a symmetrical string, that is, a string read identically from left to right as well as from right to left. You are to write a program which, given a string, determines the minimal number of characters to be inserted into the string in order to obtain a palindrome. As an example, by inserting 2 characters, the string "Ab3bd" can be transformed into a palindrome ("dAb3bAd" or "Adb3bdA"). However, inserting fewer than 2 characters does not produce a palindrome.
Input
The first line contains one integer: the length of the input string N, 3≤N≤5000. The second line contains one string with length N. The string is formed from uppercase letters from ‘A’ to ‘Z’, lowercase letters from ‘a’ to ‘z’ and digits from ‘0’ to ‘9’. Uppercase and lowercase letters are to be considered distinct.
Output
The first line contains one integer, which is the desired minimal number.
Example
Input: 5 Ab3bd Output: 2
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Aradhya:
20130528 06:25:17
nice problem :) 

nagato:
20130513 11:05:35
its the same problem as AIBOHP ....


Michal Polivka:
20130308 16:41:40
Time limit is wrong for this problem...


符号器:
20121222 20:13:44
ny 1 got AC by O(N^2)???????????


Rishi Mukherje:
20120731 12:01:50
Solving AIBOHP took a day. Solving this one took 5mins. :D 

Rajkiran Rajkumar:
20120407 18:08:52
Can you please check my code? It fails after 10 test files :( Same logic as AIBOHP but optimised. 

Santiago Palacio:
20110530 02:23:26
Does the Case matters (a != A) ? Last edit: 20110530 02:23:47 

pankaj:
20110527 07:46:28
reduction of problem is needed. 
Added by:  Gareev 
Date:  20100816 
Time limit:  0.158s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: NODEJS OBJC PERL6 VB.NET 
Resource:  IOI 2000, Day 1 