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>){
    val n = readLine()!!.toInt()
    val l = readLine()!!
    var result = 0
    for(i in 0..n-3){
        for(j in i+1..n-2){
            for(k in j+1..n-1){
                if(l[i]!=l[j]&&l[j]!=l[k]&&l[k]!=l[i]&&k-j!=j-i){
                  result ++
                }
            }
        }
    }
    println(result)
}