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 n;
string s;

int check(int mid){
  set<char> a, b;
  int ret = 0;
  for(int i=0; i<=mid; i++) a.insert(s[i]);
  for(int i=mid+1; i<n; i++) b.insert(s[i]);
  for(auto x : a){
    for(auto y : b){
      if(x == y){
        ret++;
        break;
      }
    }
  }
  return ret;
}

int main(){
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> s;
  int ans = 0;
  for(int i=0; i<n; i++){
    ans = max(ans, check(i));
  }
  cout << ans << endl;
  return 0;
}