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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
#define MAXM 100
char s[MAXM+10]; 
bool a[MAXM+10],b[MAXM+10];   
int main()
{
    int n,m,ans;  
    int i,j;
    scanf("%d",&n); 
    scanf("%s",s);
    for(i=0;i<n;i++)
	{
        a[s[i]-'a']=1; 
        memset(b,false,sizeof(b));  
        
        for(j=i+1;j<n;j++)
		{   
            b[s[j]-'a']=1;  
        }
        m=0; 
        for(j=0;j<26;j++)
		{
            if(a[j] && b[j])
			{    
                m++; 
            } 
        } 
        ans=max(ans,m); 
    }
    printf("%d",ans); 
    return 0; 
}