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 Rust (1.42.0) (judge verdict: Accepted)

use proconio::marker::{Chars};
use proconio::input;
use std::collections::HashSet;

fn main() {
  input! {
    n: usize,
    s: Chars
  };
  
  let mut max: usize = 0;
  for i in 0..=n {
    
    let mut x: HashSet<char> = HashSet::new();
    for j in 0..i {
      x.insert(s[j]);
    }
    
    let mut y: HashSet<char> = HashSet::new();
    for j in i..n {
      y.insert(s[j]);
    }
    
    let intersection: HashSet<_> = x.intersection(&y).collect();
    let size = intersection.iter().count();
    if max < size {
      max = size;
    }
  }
  
  println!("{}", max);
}