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
	var S string

	fmt.Scanf("%d", &N)
	fmt.Scanf("%v", &S)

	num := 0
	for a := 0; a < len(S); a++ {
		A := S[a]
		for b := a+1; b < len(S); b++ {
			B := S[b]
			if A == B {
				continue
			}
			for c := b+1; c < len(S); c++ {
				C := S[c]
				if C == A || C == B {
					continue
				}
				if c - b == b - a {
					continue
				}
				num++
			}
		}
	}
	fmt.Printf("%v\n", num)
}