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 JavaScript (node.js v5.12) (judge verdict: Accepted)

"use strict"

const input = require('fs').readFileSync('/dev/stdin', 'utf8').split('\n');
const N = input[0];
const S = input[1];
let max = 0;
let used = [];
for (let i = 1; i < N; i++) {
  const k = S.slice(i - 1, i);
  if (used.indexOf(k) >= 0) {
    used.splice(used.indexOf(k), 1);
  }
  for (let ii = i; ii < N; ii++) {
    if (k == S.slice(ii, ii + 1) && 0 > used.indexOf(k)) {
      used.push(k);
    }
  }
  if (used.length > max) max = used.length;
}
console.log(max);