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)

// -*- coding:utf-8-unix -*-

use proconio::input;
use proconio::marker::{Bytes, Chars};

fn main() {
    input! {
        n:i32,
        s: Chars,
    }

    let mut ans = 0;
    for i in 0..s.len() {
        let first = s[i];
        for j in (i + 1)..s.len() {
            let sec = s[j];
            for k in (j + 1)..s.len() {
                let third = s[k];
                
                if(j - i != k - j && first != sec && first != third && sec != third){
                    ans = ans + 1;
                }
                
            }
        }
    }

    println!("{}", ans);

}