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 Go (1.14.1) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var sc = bufio.NewScanner(os.Stdin)

func main() {

	var n int
	var s string

	if sc.Scan() {
		n, _ = strconv.Atoi(sc.Text())
	}

	if sc.Scan() {
		s = sc.Text()
	}

	var rgb, r, g, b int
	for i := 0; i < n; i++ {
		switch s[i] {
		case 'R':
			r++
		case 'G':
			g++
		case 'B':
			b++
		}
	}
	rgb = r * g * b

	for j := 0; j < n; j++ {
		for i := 0; i < j; i++ {
			k := j + (j - i)
			if k < n {
				if s[i] == s[j] {
					continue
				}
				if s[i] == s[k] {
					continue
				}
				if s[j] == s[k] {
					continue
				}
				rgb--
			}
		}
	}

	fmt.Print(rgb)
}