using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using static System.Console;
using static System.Math;

class program
{
    static public int mod = 1000000007;
    static void Main()
    {
        var n = rint();
        var s = rstr();
        long ct = 0;
        var isrgb = new int[n];
        var rgbct = new int[n+1,3];
        for (int i = n-1; i >= 0; i--)
        {
            rgbct[i, 0] = rgbct[i + 1, 0];
            rgbct[i, 1] = rgbct[i + 1, 1];
            rgbct[i, 2] = rgbct[i + 1, 2];
            if (s[i] == 'R')
            {
                rgbct[i, 0] = rgbct[i + 1, 0] + 1;
                isrgb[i] = 1;
            }
            if (s[i] == 'G')
            {
                rgbct[i, 1] = rgbct[i + 1, 1] + 1;
                isrgb[i] = 2;
            }
            if (s[i] == 'B')
            {
                rgbct[i, 2] = rgbct[i + 1, 2] + 1;
                isrgb[i] = 4;
            }
        }           

        for (int i = 0; i < n; i++)
        {
            for (int j = i + 1; j < n; j++)
            {                
                if (isrgb[i] != isrgb[j])
                { 
                    int ij = j - i;
                    ct += rgbct[j+1, (7 - isrgb[i] - isrgb[j]) / 2];
                    if(j+ij < n)
                        if (isrgb[j + ij] == 7 - isrgb[i] - isrgb[j])
                            ct--;
                }
            }
        }
        Write(ct);
    }

    static int pow(int a, int b) { string binary = Convert.ToString(b, 2); int bileng = binary.Length; long a_power = a; long value = 1; for (int i = bileng - 1; i >= 0; i--) { if (binary[i] == '1') { value = value * a_power % mod; } a_power = a_power * a_power % mod; } return (int)value; }
    static string rstr() { return ReadLine(); }
    static int rint() { return int.Parse(ReadLine()); }
    static long rlong() { return long.Parse(ReadLine()); }
    static string[] stra() { return ReadLine().Split(' '); }
    static char[] chara() { string[] a = stra(); string b = ""; for (int i = 0; i < a.Length; i++) { b += a[i]; } return b.ToCharArray(); }
    static int[] inta() { string[] read_str_array = ReadLine().Split(' '); int[] return_int_array = new int[read_str_array.Length]; for (int countup_i = 0; countup_i < read_str_array.Length; countup_i++) { return_int_array[countup_i] = int.Parse(read_str_array[countup_i]); } return return_int_array; }
    static long[] longa() { string[] read_str_array = ReadLine().Split(' '); long[] return_long_array = new long[read_str_array.Length]; for (long countup_i = 0; countup_i < read_str_array.Length; countup_i++) { return_long_array[countup_i] = long.Parse(read_str_array[countup_i]); } return return_long_array; }
    static double[] doublea() { string[] read_str_array = ReadLine().Split(' '); double[] return_double_array = new double[read_str_array.Length]; for (long countup_i = 0; countup_i < read_str_array.Length; countup_i++) { return_double_array[countup_i] = double.Parse(read_str_array[countup_i]); } return return_double_array; }
    static long GCD(long a, long b) { if (a < b) { long temp = a; a = b; b = temp; } if (a % b == 0) { return b; } else { long temp = b; b = a % b; a = temp; return GCD(a, b); } }
    static long LCM(long a, long b) { return a * b / GCD(a, b); }
    static void WriteArray2(int[,] a, int b, int c) { for (int i = 0; i < b; i++) { for (int j = 0; j < c; j++) { if (j != 0) Write(" "); Write(a[i, j]); } WriteLine(); } }
    static void WriteArray(int[] a, int b) { for (int i = 0; i < b; i++) { Write(" "); Write(a[i]); } WriteLine(); }
}


Measured memory_bytes: 27444