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: Time Limit Exceeded)

use std::io;
// use std::cmp;
fn main() {
    let mut s = String::new();
    io::stdin().read_line(&mut s).unwrap();
    let n:usize = s.trim().parse().unwrap();
    s.clear();
    io::stdin().read_line(&mut s).unwrap();
    let b = s.into_bytes();
    let mut sum:u32 = 0;
    for k in 2..n {
        for j in 1..k {
            if b[k] == b[j] {
                continue;
            }
            for i in 0..j {
                if j-i != k-j && b[k] != b[i] && b[i] != b[j] {
                    sum += 1;
                }
            } 
        }
    }
    println!("{}", sum);
}