##### IOI '00 - Beijing, China

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 Specification

The first line contains one integer: the length of the input string , . The second line contains one string with length . 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 Specification

The first line contains one integer, which is the desired minimal number.

#### Sample Input

```
5
Ab3bd
```

#### Sample Output

`2`

## Comments

How to get rid of RTE here! (bad_alloc)?

You've defined int as long long, so your DP vector uses up to , and even with 32-bit integers (64-bit integers are not required for this problem), it uses of memory. The memory limit is only 32 megabytes. The solution is to only store the current and previous rows, as you only need the previous row to calculate the answer for the current row. Hope this helps.