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 proconio::fastout;
use proconio::input;
#[allow(unused_imports)]
use proconio::marker::*;

#[fastout]
fn main() {
    input! {
        n: usize,
        s: Chars,
    }
    let mut r = 0;
    let mut g = 0;
    let mut b = 0;
    for c in s.iter() {
        match c {
            'R' => r += 1,
            'G' => g += 1,
            'B' => b += 1,
            _ => panic!("not match RGB"),
        }
    }

    let mut cnt = 0;
    for l in 1..n {
        for i in 0..n {
            let j = i + l;
            let k = i + l * 2;
            if k > n - 1 {
                break;
            }

            if s[i] != s[j] && s[j] != s[k] && s[k] != s[i] {
                cnt += 1;
            }
        }
    }
    println!("{}", r * g * b - cnt);
}