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 <string.h>
 
char S[105];
 
int main() {
 
	int N;
 
	scanf("%d",&N);
 
	scanf("%s",S);
 
	int len=strlen(S);
 
	int i,j;
 
	int ans=0;
 
	for(i=0;i<len;i++){
		int history[2][26]={0};
		for(j=0;j<=i;j++){
		history[0][S[j]-'a']++;
		}
		for(j=i+1;j<len;j++){
		history[1][S[j]-'a']++;
		}
		int cnt=0;
 
		for(j=0;j<26;j++){
			if(history[0][j]>0&&history[1][j]>0){cnt++;}
		}
 
		if(ans<cnt){ans=cnt;}
	}
 
	printf("%d\n",ans);
 
	return 0;
}