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>

#define INF 1e9
#define llINF 1e18
#define MOD 1e9+7
#define pb push_back
#define mp make_pair 
#define F first
#define S second
#define ll long long
using namespace std;
int main(){
  int a,b,c;
  string s1,s2;
  cin>>a;
  cin>>s1;
  int ans=0;
  for(int i=1;i<a;i++){
    bool alfa[30]={};
    bool alfa2[30]={};
    for(int j=0;j<i;j++){
      alfa[s1[j]-'a']=true;
    }
    for(int j=i;j<a;j++)
      alfa2[s1[j]-'a']=true;
    int cnt=0;int cnt2=0;
    for(int j=0;j<26;j++){
      if(alfa[j]&&alfa2[j])cnt++;
    }
    ans=max(ans,cnt);
  }
  cout<<ans<<endl;
  return 0;
}