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;
 
#define ll long long int
 
#define REP(i, n) for(int i = 0; i < (n); i++)
#define SREP(i, s) for(int i = 0; i < (s.size()); i++)
#define SORT(v, n) sort(v, v+n);
#define GSORT(v, n) sort(v, v+n, greater<int>());
#define VSORT(v) sort(v.begin(),v.end());
#define VGSORT(v) sort(v.begin(),v.end(),greater<int>());
#define REV(a) reverse(begin(a),end(a));

int main(){
	ios::sync_with_stdio(false);cin.tie(0);
////////////////////////////////////////////
	int n;
	string s;
	cin >> n >> s;
	bool lb=0;
	bool rb=0;
	int cnt=0;
	int ans=0;
	REP(i,n){
		for(char c='a';c<='z';c++){
			lb=0;rb=0;
			REP(j,i){
				if(s[j]==c) lb=1;
			}
			for(int k=i;k<n;k++){
				if(s[k]==c) rb=1;
			}
			if(lb&&rb) cnt++;
		}
		ans=max(ans,cnt);
		cnt=0;
	}
	cout << ans << endl;

/////////////////////////////////////////////
}