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<stdlib.h>
char a[101];
int b[26] = {0};
int c[26] = {0};
int main(void)
{
	
	int n;
	while (scanf("%d",&n)!=EOF)
	{
		
		scanf("%s", a);
		int max=0;
		int num=0;
		for (int i = 0; i < n; i++)
		{
			for (int m = 0; m <= i; m++)
			{
				int v = (int)a[m] - 97;
				b[v]++;
			}
			for (int j = n - 1; j > i; j--)
			{
				
				for (int q = n - 1; q >= j; q--)
				{
					int h = (int)a[q] - 97;
					c[h]++;
				}
				
				for (int l = 0; l < 26; l++)
				{
					
					if (b[l] != 0 && c[l] != 0)
					{
						num++;
						
					}
				}
				if (num > max)
					max = num;
				num = 0;
				for (int q = 0; q < 26; q++)
				{
					c[q] = 0;
				}
			}
			for (int q = 0; q < 26; q++)
			{
				b[q] = 0;
			}
		}
		printf("%d\n", max);
	}
	
	return 0;
}