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 <algorithm>
#include <string>
using namespace std;
int main(){
	int n;
	cin>>n;
	string s;
	cin>>s;
	int ans=0;
	for(int i=1;i<n;i++){
		int cnt=0;
		for(char c='a';c<='z';c++){
			bool left=false,right=false;
			for(int j=0;j<i;j++)
				if(s[j]==c){
					left=true;
					break;
				}
			for(int j=i;j<n;j++)
				if(s[j]==c){
					right=true;
					break;
				}
			if(left&&right)
				cnt++;
		}
		if(ans<cnt)
			ans=cnt;
	}
	cout<<ans<<endl;
}