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)

N = int(input())
S = input()

r=0
ListR = []
g=0
ListG = []
b=0
ListB = []
for i in range(N):
    if S[i] == 'R':
        r = r+1
        ListR.append(i)
    elif S[i] == 'G':
        g = g+1
        ListG.append(i)
    else:
        b = b+1
        ListB.append(i)
        
n = (N+1)//2
  
remove = 0
for i in range(1,n+1):
    for j in range(N-2*i):
        if S[j] != S[j+i] and S[j+i] != S[j+2*i] and S[j] != S[j+2*i]:
            remove = remove+1
            
print(r*g*b-remove)