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: Accepted)

# https://atcoder.jp/contests/abc098/tasks/abc098_b

if ARGV[0]=="LOCAL_DEV"
  define_method("debug") do |var|
    p var
  end
else
  define_method("debug") do |var|
  end
end

N=STDIN.gets.strip.to_i
S=STDIN.gets.strip
ans=0
(1..S.size-1).each do |i|
  s=S[0,i]
  t=S[i,N]
  shash = Hash.new(0)
  thash = Hash.new(0)
  s.chars do |a|
    shash[a]+=1
  end
  t.chars do |a|
    thash[a]+=1
  end
  c=0
  ('a'..'z').each do |a|
    if shash[a]>0 && thash[a]>0
      c+=1
    end
  end
  ans=[ans,c].max
end

puts ans