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: Wrong Answer)

#include <stdio.h>
#include <string.h>
#define MAX 100
int main(void) {
    int N, i, j, ans=0;
    
    char S[MAX];
    int history[2][26]={0};
    scanf("%d", &N);
    scanf("%s", S);
    
    int len = strlen(S);
    for(i=0; i<len; i++) {
        for(j=0; j<=i; j++)
            history[0][S[j]-'a']++;
        
        for(j=i+1; j<len; j++)
            history[1][S[j]-'a']++;
        
        int cnt = 0;
        for(j=0; j<26; j++) {
            if(history[0][j]>0 && history[1][j]>0)
                cnt++;
        }
        
        if(ans<cnt)
            ans = cnt;
    }
    printf("%d\n", ans);
    return 0;
}