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>

main(){
    int n;
    char str[200];

    scanf("%d",&n);
    scanf("%s",str);

    int i,j;
    int x[30],y[30];
    int max=0,c;
    for(i=0;i<=n;i++){
        for(j=0;j<30;j++)
            x[j]=y[j]=0;
        for(j=0;j<n;j++){
            if(j<i)
                x[str[j]-'a']++;
            else
                y[str[j]-'a']++;
        }
        c=0;
        for(j=0;j<30;j++)
            if(x[j]&&y[j])
                c++;
        if(max<c)
            max=c;
    }
    printf("%d\n",max);
    return 0;
}