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 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;
  for (int i=0; i<=N; i++){
    int tmp = func(S.substr(0, i), S.substr(i));
    ans = max(ans, tmp);
  }

  cout << ans << endl;
  return 0;
}