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 Fortran (gfortran v4.8.4) (judge verdict: Accepted)

program main
  implicit none
  integer :: n, i, res
  character(100) :: s, l, r
  read(*, *) n
  read(*, *) s
  res = 0
  do i = 1, n - 1  ! Cut after i-th char
    l = s(1:i)
    r = s(i + 1:n)
    res = max(res, sum(exist_mask(l) * exist_mask(r)))
  end do
  write(*, "(i0)") res

  contains

  function exist_mask(s)
    implicit none
    character(26), parameter :: abc = "abcdefghijklmnopqrstuvwxyz"
    integer :: exist_mask(26)
    character(100), intent(in) :: s
    integer :: i, j
    exist_mask(:) = 0
    do i = 1, 26
      do j = 1, 100
        if (abc(i:i) == s(j:j)) then
          exist_mask(i) = 1
        end if
      end do
    end do
  end function exist_mask
end program main