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)

// https://atcoder.jp/contests/abc098/tasks/abc098_b

#include <bits/stdc++.h>
#define REP(i, n) for (int(i) = 0; (i) < (n); (i)++)
#define REPR(i, n) for (int(i) = (n); (i) >= 0; (i)--)
#define FOR(i, m, n) for (int(i) = (m); (i) < (n); i++)
#define INF 1e9
#define ALL(v) (v).begin(), (v).end()
using namespace std;
typedef long long ll;

int ma(int p, string &s)
{
  string x = s.substr(0, p),
         y = s.substr(p);
  set<char> m;

  REP(i, p)
  {
    if (y.find(x[i]) != string::npos)
      m.insert(x[i]);
  }

  return m.size();
}

int main()
{
  /* Magic word */
  // cin.tie(0);
  // ios::sync_with_stdio(false);
  /* ---------- */

  int n;
  string s;

  cin >> n >> s;

  int p = 0, m = 0;

  while (++p < s.length())
  {
    m = max(m, ma(p, s));
  }

  cout << m << '\n';

  return 0;
}