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 Main(s){
	s=s.split(/\n/);
	s[0]|=0;
	var a=[],b=[];
	
	for(var i=0;i<s[0];i=(i+1)|0){
		b[s[1][i]]|=0;
		a[s[1][i]]|=0;
		b[s[1][i]]++;
	}
	
	var d=0
	for(var i=0;i<s[0];i=(i+1)|0){
		a[s[1][i]]++;
		b[s[1][i]]--;
		
		var c=0;
		for(var item in a){if(a[item]&&b[item]){c++;}}
		if(d<c){d=c;}
		
	}
	
	console.log(d);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));