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: Time Limit Exceeded)

package main

import "fmt"

func main() {
	var n int
	fmt.Scan(&n)
	var s string
	fmt.Scan(&s)
	fmt.Println(Calc(s))
}

func Calc(s string) int {
	var sum int
	n := len(s)
	for i := 0; i <= n-3; i++ {
		for j := i + 1; j <= n-2; j++ {
			for k := j + 1; k <= n-1; k++ {
				if s[i] != s[j] && s[i] != s[k] && s[j] != s[k] && j-i != k-j {
					sum++
				}
			}
		}
	}
	return sum
}