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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin>>n;
    string s;
    int maxi = 0;
    cin>>s;
    for(int i=1;i<s.length()-1;i++){
        int f1[26]={0}, f2[26]={0};
        for(int j=0;j<i;j++)    {f1[s[j]-'a']++;}
        //cout<<endl;
        for(int j=i;j<s.length();j++)   {f2[s[j]-'a']++;}
        int cnt = 0;
        for(int k=0;k<26;k++){
            if(f1[k]>0&&f2[k]>0)  {//cout<<k<<" ";
            cnt++;}
        }
        maxi = max(cnt,maxi);
        //cout<<maxi<<endl;
    }
    cout<<maxi;
    return 0;
}