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)

N = gets.to_i
S = gets.chomp

tbl1 = Array.new(26, 0)
tbl2 = Array.new(26, 0)

N.times do |i|
  c = S[i].ord - 'a'.ord
  tbl2[c] += 1
end

ans = 0
N.times do |i|
  c = S[i].ord - 'a'.ord
  tbl1[c] += 1
  tbl2[c] -= 1
  cnt = 26.times.count { |j| tbl1[j].positive? && tbl2[j].positive? }
  ans = [ans, cnt].max
end

puts ans