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: Accepted)

private fun readLn() = readLine()!! // string line
private fun readInt() = readLn().toInt() // single int
private fun readLong() = readLn().toLong() // single long
private fun readStrings() = readLn().split(" ") // list of strings
private fun readInts() = readStrings().map(String::toInt) // list of ints
private fun readLongs() = readStrings().map(String::toLong) // list of longs

fun main(args: Array<String>) {
    val n = readInt()
    val s = readLn().toCharArray()

    val r = s.count { it == 'R' }
    val g = s.count { it == 'G' }
    val b = s.count { it == 'B' }

    var t = (r.toLong() * g.toLong() * b.toLong())

    (0..n - 3).forEach {i ->
        (i..n - 2).forEach { j ->
            val k = 2 * j - i
            if (k < n) {
                if (s[i] != s[j] && s[j] != s[k] && s[k] != s[i]) {
                    t--
                }
            }
        }
    }
    println(t)
}