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>
#include <algorithm>
#include <map>
#include <cstdlib>
#include <cmath>
#define _GLIBCXX_DEBUG
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
typedef long long ll;

ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
ll lcm(ll a,ll b){return a/gcd(a,b)*b;}

int main(){
    int n;
    string s;
    cin >> n >> s;
    int ans=0;
    for(int i=1;i<n;i++){
        string x=s.substr(0,i);
        string y=s.substr(i);
        set<char> st;
        int tmp=0;
        for(int a=0;a<x.size();a++) st.insert(x[a]);
        for(auto p:st){
            if(y.find(p)!=string::npos) ++tmp;
        }
        ans=max(ans,tmp);
    }
    cout << ans << endl;
}