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, val, i, j, k, cnt, max, exist[26];
	char c, s[101];
	val = scanf("%d%s", &n, &s);
	if (val == 0) return 1;

	int count(){
		for (j = 0; j < 26; j++) exist[j] = 0;
		cnt = 0;
		for (j = 0; j < i; j++) {
			c = s[j];
			if (exist[c - 'a']) continue;
			else exist[c - 'a'] = 1;
			for (k = i; k < n; k++) {
				if (c == s[k]) {
					cnt++;
					break;
				}
			}
		}
		return cnt;
	}

	max = 0;
	for (i = 1; i < n; i++) {
		val = count();
		if (val > max) max = val;
	}

	printf("%d", max);
	return 0;
}