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)

function check(a,b){
	var c={},d=0;
	for(var i=0;i<a.length;i++){
		c[a[i]]=true;
	}
	for(var i=0;i<b.length;i++){
		if(c[b[i]]){
			c[b[i]]=false;
			d++
		}
	}
	return d;
}

function main(input) {
	var max=0;var a;
	var n=parseInt(input.split("\n")[0]);
	var s=input.split("\n")[1];
	for(var i=1;i<n;i++){
		a=check(s.substr(0,i), s.substr(i));
		if(a>max)max=a;
	}
	console.log(max)
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));