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 Julia (1.4.0) (judge verdict: Accepted)

N=parse(Int,readline())
S=readline()

r=0
g=0
b=0
for i in 1:N
    S[i]=='R' && (global r+=1)
    S[i]=='G' && (global g+=1)
    S[i]=='B' && (global b+=1)
end

s=0

for t in 1:(N÷2)
    for i in 1:(N-2t)
        j,k=i+t,i+2t
        if(S[i]!=S[j] && S[i]!=S[k] && S[j]!=S[k] )
            global s+=1
        end
    end
end
print(r*g*b-s)