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(void)
{
	int n,x[30][2]={0},max=0,i,j,k;
	char s[101];
	char al[26]={"abcdefghijklmnopqrstuvwxyz"};
	scanf("%d %s", &n, s);
	for(i=0; i<n-1; i++)
	{
		for(j=0; j<26; j++)
		{
			for(k=0; k<=i; k++)
			{
				if(s[k]==al[j])
				x[j][0]=1;
			}
			for(k=i+1; k<n; k++)
			{
				if(s[k]==al[j])
				x[j][1]=1;
			}
		}
		k=0;
		for(j=0; j<26; j++)
		{
			if(x[j][0]>0&&x[j][1]>0)
			k++;
			x[j][0]=0;
			x[j][1]=0;
		}
		if(max<k)
		max=k;
	}
	printf("%d\n", max);
	
	return 0;
}