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: Runtime Error)

#include <stdio.h>
#define MAX 1000
int main(void) {
    int N, cut, i, j, eqcnt=0, max=0;
    char S[MAX];
    scanf("%s", S);
    scanf("%d", &N);
    
    for(cut=0; cut<N-1; cut++) {
        eqcnt = 0;
        for(i=0; i<=cut; i++) {
            for(j=cut+1; j<N; j++) {
                if(S[i]==S[j]) {
                    eqcnt++;
                }
            }
        }
        if(eqcnt>=max) {
            max = eqcnt;
        }
    }
    printf("%d", max);
    return 0;
}