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>
#include<stdbool.h>
#include<limits.h>

bool contain(char *s, int start, int end, char c){
	for(int i=start; i<=end; i++){
		if(s[i] == c) return true;
	}
	return false;
}

int both(char *s, int dev, int n){
	int ans = 0;
	for(int i=0; i<26; i++){
		if(contain(s, 0, dev, 'a' + i) && contain(s, dev+1, n-1, 'a' + i)) ans++;
	}
	return ans;
}

int main(){
	int n;
	char s[101];
	int ans = 0;
	int tmp;
	scanf("%d\n", &n);
	scanf("%s\n", s);
	for(int i= 0; i< n; i++){
		tmp = both(s, i, n);
		if(tmp > ans) ans = tmp;
	}
	printf("%d\n", ans);
	return 0;
}