#include<bits/stdc++.h>
using namespace std;
#define mp make_pair
typedef long long ll;
const int N=40;
int n;
char s[N];
ll ans;
map<pair<string,string>,int>Map;
int main(){
	scanf("%d",&n);
	scanf("%s",s+1);
	for (int S=0;S<1<<n;S++){
		string R="",B="";
		for (int i=0;i<n;i++)
			if (S&(1<<i))R+=s[i+1];
			else B+=s[i+1];
		Map[mp(R,B)]++;
	}
	for (int S=0;S<1<<n;S++){
		string R="",B="";
		for (int i=0;i<n;i++)
			if (S&(1<<i))R+=s[2*n-i];
			else B+=s[2*n-i];
		ans+=Map[mp(R,B)];
	}
	printf("%lld\n",ans);
}

### Prompt

Develop a solution in CPP to the problem described below:

You are given a string S of length 2N consisting of lowercase English letters.

There are 2^{2N} ways to color each character in S red or blue. Among these ways, how many satisfy the following condition?

* The string obtained by reading the characters painted red from left to right is equal to the string obtained by reading the characters painted blue from right to left.

Constraints

* 1 \leq N \leq 18
* The length of S is 2N.
* S consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:


N
S


Output

Print the number of ways to paint the string that satisfy the condition.

Examples

Input

4
cabaacba


Output

4


Input

11
mippiisssisssiipsspiim


Output

504


Input

4
abcdefgh


Output

0


Input

18
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa


Output

9075135300

### Response

```cpp
#include<bits/stdc++.h>
using namespace std;
#define mp make_pair
typedef long long ll;
const int N=40;
int n;
char s[N];
ll ans;
map<pair<string,string>,int>Map;
int main(){
	scanf("%d",&n);
	scanf("%s",s+1);
	for (int S=0;S<1<<n;S++){
		string R="",B="";
		for (int i=0;i<n;i++)
			if (S&(1<<i))R+=s[i+1];
			else B+=s[i+1];
		Map[mp(R,B)]++;
	}
	for (int S=0;S<1<<n;S++){
		string R="",B="";
		for (int i=0;i<n;i++)
			if (S&(1<<i))R+=s[2*n-i];
			else B+=s[2*n-i];
		ans+=Map[mp(R,B)];
	}
	printf("%lld\n",ans);
}

```