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>
#include<math.h>
int main()
{
	char str[200];
	int n,a[200]={0},i,j,max=0,x,y,ok,t;
	scanf("%d",&n);
	scanf("%s",str);
	for(i=0;i<n;i++)
	{
		ok=1;
		if(str[i]=='0')
			continue;
		for(j=n-1;j>i;j--)
		{
			if(str[j]==str[i] && ok==1)
			{
				for(x=i;x<=j;x++) a[x]++;
				ok=0;
			}
			else if(ok==0 && str[j]==str[i])
				str[j]='0';
		}
		if(i==j && ok==1)
			str[i]='0';
	}
	for(i=0;i<n;i++)
		max=max>a[i]?max:a[i];
	printf("%d\n",max);
	return 0;
}