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: Wrong Answer)

function Main(input) {
	input = input.trim();
	var s = input.split("\n")[1];
	var max = 0;
	for(var i=0; i<s.length/2; i++){
		var a = sortMarge(s.substring(0,i+1));
		var b = sortMarge(s.substring(i+1,s.length));
		var count = 0;
		for(var j=0;j<a.length;j++){
			if(b.indexOf(a[j]) > -1){
				count++;
			}
		}
		if(max < count){
			max = count;
		}
	}
	console.log(max);
	return ;
}
function sortMarge(arg){
	var mySet = new Set();
	for(var i=0;i<arg.length;i++){
		mySet.add(arg[i]);
	}
	var array = [];
	mySet.forEach(function(value){
		array.push(value);
	})
	array.sort();
	var ret = "";
	array.forEach(function(value){
		ret+=value;
	})
	return ret;
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));