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: Wrong Answer)

function main()
    n = parse(Int, readline())
    s = readline()
    count = 0
    counts = [Int[], Int[], Int[]] #RGB
    x,y,z = 0,0,0
    for i in 1:n
        c = s[i]
        if c == 'R'
            push!(counts[1], i)
            x += 1
        elseif c == 'G'
            push!(counts[2], i)
            y += 1
        else
            push!(counts[3], i)
            z += 1
        end
    end

    for i in 1:x
        for j in 1:y
            for k in 1:z
                a,b,c = counts[1][i], counts[2][j], counts[3][k]
                if b - a == c - b
                    #カウントしない
                else
                    count += 1
                end
            end
        end
    end     

    println(count)
end

main()