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 Scala (2.11.7) (judge verdict: Accepted)

object Main {
  class Solver(n: Int, s: String) {
    def nChar: (String, String) => Int = {
      def sub: (Array[Char], Array[Char], Char) => Int  = {
        (x, y, c) => c match {
          case 'z' => {
            if (x.contains(c) && y.contains(c)) 1
            else 0
          }
          case _ => {
            if (x.contains(c) && y.contains(c)) sub(x, y, (c+1).toChar) + 1
            else sub(x, y, (c+1).toChar)
          }
        }
      }
      (x, y) => sub(x.toCharArray, y.toCharArray, 'a')
    }

    def solve: Int = {
      val li = for (i <- 1 to n-1) yield nChar(s.slice(0, i), s.slice(i, n))
      li.max
    }
  }
  
  def main(args: Array[String]): Unit = {
    val n = io.StdIn.readLine().toInt
    val s = io.StdIn.readLine()
    val solver = new Solver(n, s)
    println(solver.solve)
  }
}