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 C# (.NET Core 3.1.201) (judge verdict: Time Limit Exceeded)

using System;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = Console.ReadLine();
            var sArray = Console.ReadLine().ToCharArray();

            var count = 0;
            for (int i = 0; i < sArray.Length - 2; i++)
                for (int j = i; j < sArray.Length - 1; j++)
                    for (int k = j; k < sArray.Length; k++)
                    {
                        if (j - i == k - j) continue;
                        var si = sArray[i];
                        var sj = sArray[j];
                        if (si == sj) continue;
                        var sk = sArray[k];
                        if (si == sk || sj == sk) continue;
                        count++;
                    }
            Console.WriteLine(count);
        }
    }
}