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 PyPy3 (7.3.0) (judge verdict: Time Limit Exceeded)

n = int(input())
s_list = list(map(str,input()))
R_list=[];G_list=[];B_list=[];ans=0
 
for i in range(n):
    if s_list[i]=="R":
        R_list.append(i)
    elif s_list[i]=="G":
        G_list.append(i)
    else:
        B_list.append(i)
 
for a in R_list:
    for b in G_list:
        for c in B_list:
            if a+b==2*c or a+c==2*b or b+c==2*a:
                continue
            ans += 1
print(ans)