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 Common Lisp (SBCL 2.0.3) (judge verdict: Time Limit Exceeded)

(let ((n (read))
      (s (read-line))
      (ans 0))
  (loop :for a :from 0 :to (1- n)
        :for x := (char s a)
        :do (loop :for b :from (1+ a) :to (1- n)
                  :for y := (char s b)
                  :do (loop :for c :from (1+ b) :to (1- n)
                            :for z := (char s c)
                            :if (and (char/= x y z)
                                     (/= (- b a) (- c b)))
                            :do (incf ans))))
  (format t "~A~%" ans))