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: Time Limit Exceeded)

N=int(input())
S=input()
SS=[a for a in S]
SS.insert(0,0)
answer=0
for i in range(1,N-1):
    for j in range(i+1,N+1):
        if SS[i]==SS[j]:
            continue
        for k in range(j+1,N+1):
            if i+k==j*2:
                continue
            else:
                if SS[i]!=SS[j] and SS[j]!=SS[k] and SS[k]!=SS[i]:
                    answer+=1
print(answer)