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 Python (3.8.2) (judge verdict: Accepted)

def contains(n, s):
	r, g, b = 0, 0, 0
	for i in s:
		if i == 'R':
			r += 1
		if i == 'G':
			g += 1
		if i == 'B':
			b += 1
	ans = r * g * b
	for i in range(len(s)):
		for j in range(i + 1, len(s)):
			k = j - i + j
			if k < len(s):
				if (s[i] == 'R' or s[j] == 'R' or s[k] == 'R') and (s[i] == 'G' or s[j] == 'G' or s[k] == 'G') and (s[i] == 'B' or s[j] == 'B' or s[k] == 'B'):
					# print(i, j, k)
					ans -= 1
	return ans


n = int(input())
s = input()
print(contains(n, s))