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 Ruby (2.3.3) (judge verdict: Wrong Answer)

N = gets.chomp.to_i

S = gets.chomp.split("")

def include_both(a1, a2)
  a1.sort!.uniq!
  a2.sort!.uniq!

  count = 0

  for i in 0...a1.length do
    for j in 0...a2.length do
      if a1[i] == a2[j] then
        count += 1
        break
      end
    end
  end
  
  count
end

max = 0
for i in 1..((N/2)+1) do
  s1 = S[0, i]
  s2 = S[i, N-1]

  max = [max, include_both(s1, s2)].max
end

puts max