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 (2.7.1) (judge verdict: Wrong Answer)

n = gets.chomp.to_i
s = gets.chomp.split("")
a = []
b = s
ans = 0
(n-1).times do 
    hash_a = Hash.new(0)
    hash_b = Hash.new(0)
    a << b.shift
    a.each do |i|
        hash_a[i] += 1
    end
    b.each do |i|
        hash_b[i] += 1
    end
    max = [hash_b.size,hash_a.size].max
    min = [hash_b.size,hash_a.size].min
    if max == hash_b.size
        big = hash_b
        small = hash_a
    elsif max == hash_a
        big = hash_a
        small = hash_b
    end
    if big == nil || small == nil
        break
    end
    #  p big
    #  p small
    count = 0
    small.each do |i|
        # p big[i[0]]
        if big.include?(i[0]) 
            count += 1
           # [i[1],big[i[0]]].min
        end
    end
    ans = [ans,count].max
end
puts ans