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 C (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>
int main(){

	int n,i,j,k,d=0,c;
	char s[101];

	scanf("%d%s",&n,s);

	for(i=2;i<n-1;i++){
		char x[27]={},y[27]={};

		for(j=0;j<n;j++){
			if(j<i)
				x[s[j]-'a']=1;
			else
				y[s[j]-'a']=1;
		}
		c=0;
		for(k=0;k<27;k++){
			if(x[k]==y[k])
				c+=x[k];
		}
		if(c>d)
			d=c;
	}
	printf("%d",d);
	return 0;
}