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>
#include <algorithm>

using namespace std;

#define ll long long

int N, ans = 0;
string S;

void solve(){
    for(int i = 1; i < N;i++){
        int cnt = 0;
        string X = S.substr(0,i);
        string Y = S.substr(i,N-i);
        for(int j = 0; j < 27; j++){
            char buff = 'a'+j;
            if(X.find(buff) != string::npos && Y.find(buff) != string::npos) cnt++;
        }
        ans = max(ans, cnt);
    }
    cout << ans << endl;
}

int main(){
    cin >> N >> S;

    solve();
}