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 Scala (2.13.1) (judge verdict: Time Limit Exceeded)

import scala.io.StdIn._
object Main extends App{
  val N = readLine().toInt
  val S = readLine()

  var sum = 0
  (0 until N-2).foreach(i => {
    (i+1 until N-1).foreach(j => {
      (j+1 until N).foreach(k => {
        val si = S(i)
        if((si != S(j)) && (S(i) != S(k)) && (S(j) != S(k)) && ((j-i) != (k-j))){
          sum = sum + 1
        }
      })
    })
  })

  println(sum)
}