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<time.h>
#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<iomanip>
#include<math.h>
#include<complex>
#include<queue>
#include<deque>
#include<stack>
#include<map>
#include<set>
#include<bitset>
#include<functional>
#include<assert.h>
#include<numeric>
using namespace std;
#define REP(i,m,n) for(int i=(int)(m) ; i < (int) (n) ; ++i )
#define rep(i,n) REP(i,0,n)
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
using ll = long long;
using vi = vector<int>;
using vvi = vector<vector<int>>;
using vll = vector<ll>;
using vvll = vector<vector<ll>>;
const int inf=1e9+7;
const ll longinf=1LL<<60 ;
const ll mod=1e9+7 ;
using namespace std;
struct Fast { Fast(){ std::cin.tie(0); ios::sync_with_stdio(false); } } fast;

template<typename ...Ts>
void show(Ts... ts){
  cout<<"#:";
  auto print=[](auto v){cout<<v<<" ";};
  initializer_list<int>{(void(print(ts)),0)...};
  cout<<endl;
}

int main(void){
    int n,ans=0;
    string s;
    cin>>n>>s;
    int m[26],tmp;
    

    rep(c,n){
        rep(i,26)m[i]=0;
        tmp=0;
        rep(i,c){
            REP(j,c,n){
                if (s[i]==s[j]){
                    if (m[s[i]-'a']==0)tmp+=1;
                    m[s[i]-'a']=1;
                }
            }
        }
        ans=max(ans,tmp);
    }
    cout<<ans;
}