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() {
  int number_n, i, j, answer = 0, flag, count;
  char ch;
  scanf("%d", &number_n);
  char str[number_n+1];
  scanf("%s", str);
  for(i = 0; i < number_n-1; i++) {
    count = 0;
    for(ch = 'a'; ch <= 'z'; ch++) {
      flag = 0;
      for(j = 0; j <= i; j++) {
        if(str[j] == ch) flag = 1;
      }
      if(flag == 0) continue;
      for(j = i + 1; j < number_n; j++) {
        if(str[j] == ch) flag = 2;
      }
      if(flag == 2) count++;
    }
    answer = (count > answer)? count : answer;
  }
  printf("%d\n", answer);
  return 0;
}