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 <iostream>
#include <string>

using namespace std;

int main()
{
    int n, ans=0, a[26], b[26], c;
    string s;
    cin>>n>>s;
    for (int i=0; i<n-1; i++)
    {
        c=0;
        for (int j=0; j<26; j++) { a[j]=0; b[j]=0; }
        for (int j=0; j<=i; j++) a[s[j]-'a']=1;
        for (int j=i+1; j<n; j++) b[s[j]-'a']=1;
        for (int j=0; j<26; j++)
        {
            if (a[j] && b[j]) c++;
        }
        ans=max(ans, c);
    }
    cout<<ans<<endl;
    return 0;
}