Problem:
Score : 900 points

Problem Statement

Takahashi has decided to give a string to his mother.

The value of a string T is the length of the longest common subsequence of T and T', where T' is the string obtained by reversing T.
That is, the value is the longest length of the following two strings that are equal: a subsequence of T (possibly non-contiguous), and a subsequence of T' (possibly non-contiguous).

Takahashi has a string S. He wants to give her mother a string of the highest possible value, so he would like to change at most K characters in S to any other characters in order to obtain a string of the highest possible value.
Find the highest possible value achievable.

Constraints

1 \leq |S| \leq 300

0 \leq K \leq |S|

S consists of lowercase English letters.

K is an integer.

Input

Input is given from Standard Input in the following format:

S
K

Output

Print the highest possible value achievable.

Sample Input 1

abcabcabc
1

Sample Output 1

7

Changing the first character to c results in cbcabcabc.
Let this tring be T, then one longest common subsequence of T and T' is cbabcbc, whose length is 7.

Sample Input 2

atcodergrandcontest
3

Sample Output 2

15

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <algorithm>
using namespace std;

int n,m,i,j,k,l,r;
int f[305][305][305];
char s[100005];

int main()
{
	scanf("%s",s+1);n=strlen(s+1);
	scanf("%d",&m);
	for(i=1;i<=n;++i)
	for(j=0;j<=m;++j)
	f[i][i][j]=1;
	for(i=1;i<n;++i)
	for(l=1;l+i<=n;++l)
	{
		r=l+i;
		for(j=0;j<=m;++j)
		{
			f[l][r][j]=max(f[l+1][r][j],f[l][r-1][j]);
			if(s[l]==s[r])f[l][r][j]=max(f[l][r][j],f[l+1][r-1][j]+2);
			else if(j)f[l][r][j]=max(f[l][r][j],f[l+1][r-1][j-1]+2);
		}
	}
	printf("%d\n",f[1][n][m]);
}