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++ (GCC 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
using namespace std;
using ll = long long;
using P = pair<int,int>;

int main() {
  int n;
  string s;
  cin >> n >> s;
  int ans = 0;
  for(int i = 1; i < n; i++) {
    int cnt = 0;
    for(char c = 'a'; c <= 'z'; c++) {
      bool left = false;
      bool 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(left && right) cnt++;
    }
    ans = max(ans, cnt);
  }
  cout << ans << endl;
  return 0;
}