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<bits/stdc++.h>
using namespace std;

// macro
#define rep(i,n) for(i=0;i<n;i++)
#define ll long long
#define all(v) v.begin(), v.end()

// code starts
int main()
{
	int n;cin>>n;
	string s;cin>>s;
	int i,j;
	int ans=0;
	rep(i,n+1)
	{
		string x=s.substr(0,i);
		string y=s.substr(i,n-i);
		vector<bool> alpx(26);
		vector<bool> alpy(26);
		rep(j,x.size())
		{
			alpx[x[j]-'a']=true;
		}
		rep(j,y.size())
		{
			alpy[y[j]-'a']=true;
		}
		int kans=0;
		rep(j,26)if(alpx[j]&&alpy[j])kans++;
		ans=(kans>ans)?kans:ans;
	}
	cout<<ans<<endl;
}