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: Wrong Answer)

using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;

namespace D
{
    public class Program
    {
        static void Main(string[] args)
        {
            var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);
            Solve();
            Console.Out.Flush();
        }

        public static void Solve()
        {
            var n = int.Parse(Console.ReadLine());
            var s = Console.ReadLine();
            var r = 0;
            var g = 0;
            var b = 0;
            for (var i = 0; i < s.Length; i++)
            {
                switch (s[i])
                {
                    case 'R': r++; break;
                    case 'G': g++; break;
                    case 'B': b++; break;
                }
            }
            var count = r * g * b;
            for (var i = 0; i < n; i++)
            {
                for (var j = i + 1; j < n; j++)
                {
                    var k = 2 * j - i;
                    if (k <= j || k >= n) continue;
                    if (s[i] != s[j] && s[i] != s[k] && s[j] != s[k]) count--;
                }
            }
            Console.WriteLine(count);
        }
    }
}