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 (GCC 5.4.1) (judge verdict: Time Limit Exceeded)

#include <stdio.h>


void shokika(void);

int i;
char s1[100];

int main(int argc, char **argv)
{
  int n;
  shokika();
  scanf("%d",&n);
  int j,k,l,xxx;
  int x[n];
  char s[n + 1];
  scanf("%s",s);
  for(j = 0 ; j < n ; j++){
    for(k = 0 ; k < j + 1 ; k++){
      s1[k] = s[k];
    }
    for(k = 0 ; k < j ; k++){
      for(l = k ; l < j ; l++){
        if(s1[l] == s1[l + 1]){
          s1[l + 1] = '1';
        }
      }
    }
    for(k = 0 ; k < j + 1 ; k++){
      for(l = k ; l < n ; l++){
        xxx = 0;
        while(xxx == 0){
          if(s1[k] == s[l + 1]){
            xxx = 1;
            x[j]++;
          }
        }
      }
    }
    shokika();
  }
  for(j = 0 ; j < n ; j++){
    for(l = j ; l < n ; l++){
      if(x[l] < x[l+1]){
        xxx = x[l];
        x[l] = x[l + 1];
        x[l + 1] = xxx;
      }
    }
  }
  printf("%d\n",x[n - 1]);
  return 0;
}

void shokika(void){
  for(i = 0 ; i < 100 ; i++){
    s1[i] = '0';
  }
}