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 rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(v) (v).begin(),(v).end()
#define out(a) cout << (a) << endl
using namespace std;
using ll = long long;
int main(){
    int n;
    string s;
    int ans=0;
    cin >> n >> s;
    for (int i=1; i<n; i++){
        int cnt=0;
        for (char c='a'; c<='z'; c++){
            bool left=false, right=false;
            for(int j=0; j<i; j++){
                if (s[j] == c) left = true;
            }
            for (int j=i; j<n; j++){
                if (s[j] == c) right = true;
            }
            if(right && left) cnt++;
        }
        ans = max(cnt, ans);
    }
    out(ans);

}