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: Wrong Answer)

N = int(input())
S = list(input())
f=0
ijk = [[i+1,j+1,k+1]for i in range(N) for j in range(N) for k in range(N) 
        if i<j<k and S[i]!=S[j]!=S[k]]
# print(ijk)
for i in range(len(ijk)):
    if(ijk[i][1]-ijk[i][0] != ijk[i][2]-ijk[i][1]):
        f+=1
print(f)