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: Accepted)

#include<stdio.h>

int main()
{
  char s[100];
  int N;
  scanf("%d",&N);
  scanf("%s",s);

  int alpha[1000];
  int i,j,k,count=0,count_max=0;;

  for(i=1;i<N;i++){
    count=0;
    for(j=0;j<1000;j++){
      alpha[j]=0;
    }

    for(j=i;j<N;j++){ //後半(iから)
      for(k=0;k<i;k++){ //前半(iまで)
        if(s[j]==s[k] && alpha[s[j]]==0){
          count++;
          alpha[s[j]] = 1;
        }
      }
    }
    if(count>=count_max){
      count_max=count;
    }
  }

  printf("%d\n",count_max);

  return 0;
}