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>
#define ll long long
using namespace std;
#define rep(i, n) for (int i = 0; i < n; i++)
using P = pair <int, int>;

int func(string s,string t){
    int ans = 0;
    for(char c= 'a';c<='z';c++){
        bool founds=false, foundt = false;
        for(int i = 0;i<s.length();i++){
            if(s[i]==c){
                founds = true;
            }
        }
        for(int i = 0;i<t.length();i++){
            if(t[i]==c){
                foundt = true;
            }
        }
        if(founds && foundt) ans++;
    }
    return ans;
}

int main(){
    int N;
    string s;
    cin >> N >> s;
    int ans = 0;

    rep(i,N){
        int tmp = func(s.substr(0,i),s.substr(i));
        ans = max(ans,tmp);
    }
    cout << ans << endl;
}