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: Runtime Error)

#include<stdio.h>
#include<string.h>

int check(char str2[], char str[]);
void move(char str3[]);

int main(void){
	int n;
	scanf("%d", &n);
	
	char str[n];
	scanf("%s", str);
	
	int i;
	int j=0;
	int c_max;
	int max;
	char str2[50] = {'\0'};
	char str3[50] = {'\0'};
	str2[j++] = str[0];
	for(i=0;i<n;i++){
		str3[i] = str[i+1];
	}
	max = check(str2, str3);
	for(i=1;i<=(n-1)/2;i++){
		if(strchr(str2, str[i]) == NULL){
			str2[j++] = str[i];
		}
		str3[i-1]=str2[0];
		c_max = check(str2, str3);
		if(max <= c_max){
			max = c_max;
		}
	}
	printf("%d", max);
	return 0;
}

int check(char str2[], char str[]){
	int i;
	int j;
	int cnt = 0;
	for(i=0;str2[i]!='\0';i++){
		if(strchr(str, str2[i]) != NULL){
			cnt+=1;
		}
	}
	return cnt;
}

void move(char str3[]){
	int i;
	for(i=1;str3[i]!='\0';i++){
		str3[i-1] = str3[i];
	}
}