Problem:
Score : 200 points

Problem Statement

You are given a string S of length N consisting of lowercase English letters.
We will cut this string at one position into two strings X and Y.
Here, we would like to maximize the number of different letters contained in both X and Y.
Find the largest possible number of different letters contained in both X and Y when we cut the string at the optimal position.

Constraints

2 \leq N \leq 100

|S| = N

S consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the largest possible number of different letters contained in both X and Y.

Sample Input 1

6
aabbca

Sample Output 1

2

If we cut the string between the third and fourth letters into X = aab and Y = bca, the letters contained in both X and Y are a and b.
There will never be three or more different letters contained in both X and Y, so the answer is 2.

Sample Input 2

10
aaaaaaaaaa

Sample Output 2

1

However we divide S, only a will be contained in both X and Y.

Sample Input 3

45
tgxgdqkyjzhyputjjtllptdfxocrylqfqjynmfbfucbir

Sample Output 3

9

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

#include <cstdio>
#include <string>
#include <iostream>
#include <cmath>
#include <vector>
#include <stack>

using namespace std;


int main(void) {

	// a = 97 (int)

	char st1set[25] = { 0 };
	char st2set[25] = { 0 };

	string S;
	int N;
	int comCnt = 0;
	int max = 0;


	cin >> N;
	
	S.resize(N);

	cin >> S;

	for (int i = 0; i < N; i++) {
		for(int j = 0; j < i; j++)
			st1set[S[j] - 97] = 1;

		for (int j = i + 1; j < N; j++)
			st2set[S[j] - 97] = 1;

		for (int k = 0; k < 25; k++) {
			if (st1set[k] && st2set[k])
				comCnt++;
		}

		if (max < comCnt) {
			max = comCnt;
		}

		for (int k = 0; k < 25; k++) {
			st2set[k] = 0;
			st1set[k] = 0;
		}
		comCnt = 0;
	}

	cout << max << endl;
	
	return 0;
}