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'

function main(input) {
    input = input.split("\n");
    const N = parseInt(input[0]);
    const S = input[1];
    let ans = 0;
    for (let i = 0; i < N; i++) {
        let count = 0;
        let obj = {};
        for (let j = 0; j < i; j++) {
            obj[S[j]] = true;
        }
        for (let j = i; j < N; j++) {
            if (obj[S[j]]) {
                count++;
                delete obj[S[j]];
            }
        }
        if (count > ans)
            ans = count;
    }
    console.log(ans);
}

main(require('fs').readFileSync('/dev/stdin', 'utf-8'));