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 <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <cmath>
#include <algorithm>
#include <functional>
#include <stack>
#include <queue>
#include <map>
#include <unordered_map>
#include <bitset>
#include <numeric>
#include <unordered_set>
#include <bitset>
#include <limits>
#include <random>
#include <complex>
#include <numeric>
#include <cstdlib>
#include <random>
#include <bits/stdc++.h>


using namespace std;
typedef long long ll;
typedef pair<ll,ll> P;
typedef vector<ll> vec;
typedef vector<vec> mat;

const ll mod=1000000007ll;
const ll inf=1000000000000000ll;

const ll MAX_N=100010;

ll dp[MAX_N];

ll l_last,N;

string s;

string alp="abcdefghijklmnopqrstuvwxyz";

int main(){
  cin>>N>>s;
  ll ans=0;
  for(l_last=1;l_last<N-1;l_last++){
    ll tmp=0;
    for(ll i=0;i<26;i++){
      bool lfl=false,rfl=false;
      for(ll j=0;j<l_last;j++){
        if(s[j]==alp[i])lfl=true;
      }
      for(ll j=l_last;j<N;j++){
        if(s[j]==alp[i])rfl=true;
      }
      if(lfl&&rfl)tmp++;
    }
    ans=max(ans,tmp);
  }
  cout<<ans<<endl;
  return 0;
}