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 9.2.1) (judge verdict: Wrong Answer)

#include<stdio.h>

void init_alpha(char*);

int main(){
  int N,cut=1,ans=0;
  scanf("%d",&N);
  getchar();
  char S[N];
  char alpha[25];
  init_alpha(alpha);
  for (int i = 0; i < N; i++)
  {
    scanf("%c",&S[i]);
  }
  
  while (cut<N)
  {
    for (int x = 0; x < cut; x++){
      for (int y = cut; y < N; y++){
        if (S[x]==S[y])
        {
          alpha[S[x]-97]=1;
        }
      }
    }
    int count=0;
    for (int i = 0; i < 25; i++)
    {
      if (alpha[i]==1){ count++;}
    }
    if (ans<count){ans=count;}
    init_alpha(alpha);
    cut++;
  }
  
  
  printf("%d",ans);

  return 0;
}

void init_alpha(char *al){
  for (int i = 0; i < 25; i++){
    al[i]=0;
  }
}