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++ (GCC 9.2.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
typedef long long ll;
#define _GLIBCXX_DEBUG
typedef vector<int> vec;
typedef vector<ll> lvec;
typedef vector<char> cvec;
typedef vector<double> dvec;
typedef pair<ll, ll> LP;
typedef tuple<ll, ll, ll> LT;
typedef pair<int, int> P;
typedef tuple<int, int, int> T;
#define fs first
#define sc second
int main()	{
  string s,a,b;
  int n;
  cin>>n;
  cin>>s;
  int ans=0;
  rep(i,n){
    a=s.substr(0,i);
    b=s.substr(n-i);
    int res=0;
    vector<int>cnt1(26),cnt2(26);
    rep(j,a.size()){
      cnt1[a[j]-'a']++;
    }
    rep(j,b.size())
      cnt2[b[j]-'a']++;
    rep(j,26){
      if(cnt1[j]>0 && cnt2[j]>0)
        res++;
    }
    ans=max(ans,res);
  }
  cout<<ans<<endl;
}