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<iostream>
#include<string>

using namespace std;

int main(){
    
    int N;
    cin>>N;
    string s;
    cin>>s;
    int ans=0;
    
    for(int i=1;i<N-1;i++){
        int count =0;
        for(char c='a';c<='z';c++){
            bool right=false,left=false;
            for(int j=0;j<=i;j++){
                if(s[j]==c)left=true;
            }
            
            for(int j=i+1;j<N;j++){
                if(s[j]==c)right=true;
            }
            
            if(left&&right)count++;
        }
        if(ans<count)ans=count;
    }
    
    cout<<ans<<endl;
    
    return 0;
}