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;
    char S[101];
    int tmp[30];
    int i, j, k, l;
    int max = 0, cnt;

    scanf("%d%s", &N, S);
    for (i = 1; i < N-2; i++) {
        cnt = 0;
        for (j = 0; j < i; j++) {
            for (k = i; k < N; k++) {
                if (S[j] == S[k]) {
                        if (cnt == 0) {
                            tmp[0] = j;
                            cnt++;
                        }
                        else {
                            for (l = 0; l < cnt; l++) {
                                if (S[tmp[l]] == S[j]) break;
                            }
                            if (l == cnt) {
                                tmp[l] = j;
                                cnt++;
                            }
                        }
                }
            }
        }
        if (max < cnt) max = cnt;
    }
    printf("%d\n", max);

    return 0;
}