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(void)
{
    int n;
    scanf("%d",&n);

    char s[n];
    scanf("%s",s);

    int a[26];
    int b[26];

    int count=0;
    int max=0;
    for(int i=0; i<n-1; i++){
      for(int p=0; p<26; p++){
          a[p] = 0;
          b[p] = 0;
      }
      for(int j=0; j<i+1; j++){
        a[s[j]-'a']++;
      }
      for(int k=i+1; k<n; k++){
        b[s[k]-'a']++;
      }
      for(int l=0; l<26; l++){
        if((a[l]!= 0)&&(b[l]!=0)){
          count++;
        }
      }
      if(count>max){
        max=count;
      }
      count = 0;
    }

    printf("%d",max);
    return 0;

}