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.chomp.to_i
a = []
a = gets.split("")
b = []
c = []
cnt = []
t = 0
alp = ('a'..'z').to_a
for i in 0..n-1
t = 0
b = []
c = []
  for j in 0..i
  b.push(a[j])
  end
  for j in i+1..n-1
  c.push(a[j])
  end
 b.uniq!
 c.uniq!
  #puts b.join("")
  #puts c.join("")
  for j in 0..25
  #puts j
  #puts t
  #puts alp[j]
    if b.include?(alp[j])
        if c.include?(alp[j])
      t = t + 1
        end
    end
  end
  #puts t
  cnt.push(t)
end
 
#puts cnt.join (" ")
puts cnt.max