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: Runtime Error)

fun main() {
    val n = readLine()!!.toInt()
    val s = readLine()!!

    val rgb = s.groupBy { it }.map { it.value.size.toLong() }

    val exclude = (0..n-3).sumBy { l ->
        (1..n).count { w ->
            val c = l + w
            val r = c + w
            r < n && s[l] != s[c] && s[c] != s[r] && s[r] != s[l]
        }
    }

    println(rgb[0] * rgb[1] * rgb[2] - exclude)
}