ABAB

use itertools::Itertools;

use proconio::{*, marker::Bytes};

​

fn main() {

    input! {

        n: usize,

        s: Bytes,

    }

    let s = s.iter().map(|c| (c - b'a') as usize).collect_vec();

​

    let mut count_out = vec![0; 26];

    for i in 1..n {

        count_out[s[i]] += 1;

    }

    let mut ans: u64 = 0;

    for i in 0..n-1 {

        let mut count_in = vec![0; 26];

        for j in i+1..n {

            count_out[s[j]] -= 1;

            if s[i] == s[j] {

                for k in 0..26 {

                    ans += count_in[k] * count_out[k];

                }

            }

            count_in[s[j]] += 1;

        }

​

        count_in[s[i+1]] -= 1;

        count_out = count_in;

    }

​

    println!("{}", ans);

}

​