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,max,count;
    max=0;
    scanf("%d",&n);
    
    char s[n+1];
    scanf("%s",s);
    
    for(int i=0; i<n; i++){
        count=0;
        int a[26]={};
        
        for(int j=0; j<i; j++)
            a[s[j]-'a']=1;
        
        for(int j=i; j<n; j++){
            if(a[s[j]-'a']==1){
                count++;
                a[s[j]-'a']=0;
            }
        }
        if(max<count)
            max=count;
    }
    printf("%d",max);
}