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 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;
int main(void){
    int i=0,n,d,j,k,saidai=0,c=0,l;
    string s;
    bool used[26];
    cin >> n >> s;
    for(i=0;i<n;i++)
    {
        for(l=0;l<26;l++)
        {
            used[l]=false;
        }
        for(j=0;j<i;j++)
        {
            char h=s.at(j);
            if(used[h-'a']==false)
               {
                   used[h-'a']=true;
               }
            else
            {
                continue;
            }
            for(k=i;k<n;k++)
            {
                if(s.at(j)==s.at(k) )
                {
                    c++;
                    break;
                }
            }
        }
        if(saidai<c)
        {
            saidai=c;
        }
        c=0;
    }
    cout << saidai << endl;
    return 0;
}