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 name
    implicit none
    character(:),allocatable:: s
    integer(4):: n,i,cnt

    read*, n
    allocate(character(n):: s)
    read*, s
    cnt = 0
    do i=1,n-1
        cnt = max(cnt,snum(s(1:i), s(i+1:n)))
    end do
    print*, cnt

contains
function snum(s1, s2) result(ret)
    implicit none
    character(*):: s1, s2
    integer(4):: ret,i
    logical:: is1(ichar('a'):ichar('z')),is2(ichar('a'):ichar('z'))

    is1(:) = .false.
    is2(:) = .false.
    do i=1,len(s1)
        is1(ichar(s1(i:i))) = .true.
    end do
    do i=1,len(s2)
        is2(ichar(s2(i:i))) = .true.
    end do

    ret = 0
    do i=ichar('a'),ichar('z')
        if (is1(i) .and. is2(i)) ret=ret+1
    end do
end function snum
end program name