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)

function main()
    n = parse(Int, readline())
    s = readline()
    count = 0
    counts = [Int[], Int[], Int[]] #RGB
    x,y,z = 0,0,0
    hoge = 0
    for i in 1:n
        aa = min(i-1, n-i)
        for j in 1:aa
            if s[i] != s[i-j] != s[i+j] != s[i]
                # println(s[i], s[i-j], s[i+j])
                hoge += 1
            end
        end
        c = s[i]
        if c == 'R'
            x += 1
        elseif c == 'G'
            y += 1
        else
            z += 1
        end
    end
    println(x*y*z-hoge)
end

main()