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 Kotlin (1.3.71) (judge verdict: Time Limit Exceeded)

fun main (args: Array<String>) {
  readLine()!!.toInt()
  val s = readLine()!!.map {it - 'A'}

  var ans = 0
  for (a in 0 until s.size - 2) {
    for (b in a until s.size - 1) {
      for (c in b until s.size) {
        if (s[a] != s[b] && s[b] != s[c] && s[c] != s[a]) {
          if (b - a != c - b) {
            ans++
          }
        }
      }
    }
  }
  println(ans)
}