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>
#include<string.h>

int main(void)
{
  int n;
  char s[128];
  scanf("%d",&n);
  scanf("%s",s);
  int max=0;

  for(int i=1;i<n;i++){
    int count=0;
    for(char c='a';c<='z';c++){
      int flag1=0,flag2=0;
      for(int j=0;j<i;j++){
        if(s[j]==c){
          flag1=1;
        }
      }
      for(int k=i;k<n;k++){
        if(s[k]==c){
          flag2=1;
        }
      }
      if(flag1==1&&flag2==1){
        count++;
      }
    }
    if(count>max){
      max=count;
    }
  }


  printf("%d\n",max);
  return 0;
}