Problem:
Score : 400 points

Problem Statement

We have a string S of length N consisting of R, G, and B.

Find the number of triples (i,~j,~k)~(1 \leq i < j < k \leq N) that satisfy both of the following conditions:

S_i \neq S_j, S_i \neq S_k, and S_j \neq S_k.

j - i \neq k - j.

Constraints

1 \leq N \leq 4000

S is a string of length N consisting of R, G, and B.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the number of triplets in question.

Sample Input 1

4
RRGB

Sample Output 1

1

Only the triplet (1,~3,~4) satisfies both conditions. The triplet (2,~3,~4) satisfies the first condition but not the second, so it does not count.

Sample Input 2

39
RBRBGRBGGBBRRGBBRRRBGGBRBGBRBGBRBBBGBBB

Sample Output 2

1800

Solution in Rust (1.42.0) (judge verdict: Wrong Answer)

use std::io;

fn main() {
    let mut buf = String::new();
    io::stdin().read_line(&mut buf).unwrap();

    let n: usize = buf.trim().parse().unwrap();
    let s: Vec<String> = {
        buf = String::new();
        io::stdin().read_line(&mut buf).unwrap();
        buf.trim().chars().map(|c| c.to_string()).collect()
    };

    let mut r_count = 0;
    let mut g_count = 0;
    let mut b_count = 0;

    for i in 0..n {
        let rgb: &str = &s[i];
        match rgb {
            "R" => r_count += 1,
            "G" => g_count += 1,
            "B" => b_count += 1,
            _ => (),
        }
    }

    let mut count = r_count * g_count * b_count;

    for i in 0..n {
        let mut j = i + 1;
        let mut k = i + 2;
        while k < n {
            if s[i] != s[j] && s[j] != s[k] && s[i] != s[k] {
                count -= 1;
            }
            j += 1;
            k = j + (j - i);
        }
    }

    println!("{}", count);
}