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)

//wls niubi!
#include<bits/stdc++.h>
#define LL long long
using namespace std;
const LL mod = 1e9 + 7;
inline int read()
{
	int x = 0,f = 1;char ch = getchar();
	for(;!isdigit(ch);ch = getchar())if(ch == '-')f = -f;
	for(;isdigit(ch);ch = getchar())x = 10 * x + ch - '0';
	return x * f;
}
int n,K;
char ch[310];
int f[310][310][310];
int main()
{
	scanf("%s",ch + 1);n = strlen(ch + 1);K = read();
	for(int i=1;i<=n;i++)for(int j=0;j<=K;j++)f[i][i][j] = 1;
	for(int l=2;l<=n;l++)
	{
		for(int i=1;i+l-1<=n;i++)
		{
			int j = i + l - 1;
			for(int k=0;k<=K;k++)
			{
			    f[i][j][k] = max(f[i + 1][j][k],f[i][j - 1][k]);
			    if(ch[i] == ch[j])f[i][j][k] = max(f[i][j][k],f[i + 1][j - 1][k] + 2);
			    if(k)f[i][j][k] = max(f[i][j][k],f[i + 1][j - 1][k - 1] + 2);
			}
		}
	}
	int ans = 0;
	cout<<f[1][n][K];
}