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 n;
    scanf("%d", &n);
    char s[111];
    scanf("%s", s);
    int i, j, k, x;
    int max = 0;
    for (i = 0; i < n - 1; i++)
    {
        x = 0;
        for (j = 0; j < 26; j++)
        {
            int p;
            p = 0;
            for(k=0;k<=i;k++)
                if (s[k] == 'a' + j)
                {
                    p++;
                    break;
                }
            if (p == 0)
                continue;
            p = 0;
            for(k=i+1;k<n;k++)
                if (s[k] == 'a' + j)
                {
                    p++;
                    break;
                }
            if (p > 0)
                x++;
        }
        if (max < x)
            max = x;
    }
    printf("%d\n", max);
    return 0;
}