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

class MainClass : Scanner
{
    static void Main()
    {
        int N = RInt();
        var S = RString();
        var R = new int[N + 1];
        var G = new int[N+1];
        var B = new int[N+1];
        for (int i = N-1; i >= 0; i--)
        {
            char c = S[i];
            R[i] = R[i + 1];
            G[i] = G[i + 1];
            B[i] = B[i + 1];
            if (c == 'R') R[i]++;
            else if (c == 'G') G[i]++;
            else B[i]++;
        }
        long ans = 0;
        for (int i = 0; i < N-2; i++)
        {
            for (int j = i + 1; j < N - 1; j++)
            {
                var s = new List<char>() { 'R', 'G', 'B' };

                if (S[i] == S[j]) continue;
                s.Remove(S[i]);
                s.Remove(S[j]);

                long cnt = 0;
                if (s[0] == 'R') cnt = R[j];
                else if (s[0] == 'G') cnt = G[j];
                else cnt = B[j];

                if (2 * j - i >= j&&2*j-i<N && S[2 * j - i] == s[0]) cnt--;
                ans += cnt;
            }
        }
        WriteLine(ans);
        
    }
}



class Scanner
{
    public static string RString() => Console.ReadLine();
    public static int RInt() => ReadTuple<int>();
    public static long RLong() => ReadTuple<long>();
    public static double RDouble() => ReadTuple<double>();

    public static string[] RStrings() => Console.ReadLine().Split();
    public static int[] RInts() => Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
    public static long[] RLongs() => Array.ConvertAll(Console.ReadLine().Split(), long.Parse);
    public static double[] RDoubles() => Array.ConvertAll(Console.ReadLine().Split(), double.Parse);
    public static int[] RInts(Func<string, int> func) => Console.ReadLine().Split().Select(func).ToArray();
    public static long[] RLongs(Func<string, long> func) => Console.ReadLine().Split().Select(func).ToArray();
    public static double[] RDoubles(Func<string, double> func) => Console.ReadLine().Split().Select(func).ToArray();
    //public static string[] RStrings(Func<string, string> func) => Console.ReadLine().Split().Select(func).ToArray();

    public static T1 ReadTuple<T1>()
    {
        var r = RString();
        var r1 = (T1)Convert.ChangeType(r, typeof(T1));
        return r1;
    }
    public static (T1, T2) ReadTuple<T1, T2>()
    {
        var r = RStrings();
        var r1 = (T1)Convert.ChangeType(r[0], typeof(T1));
        var r2 = (T2)Convert.ChangeType(r[1], typeof(T2));
        return (r1, r2);
    }
    public static (T1, T2, T3) ReadTuple<T1, T2, T3>()
    {
        var r = RStrings();
        var r1 = (T1)Convert.ChangeType(r[0], typeof(T1));
        var r2 = (T2)Convert.ChangeType(r[1], typeof(T2));
        var r3 = (T3)Convert.ChangeType(r[2], typeof(T3));
        return (r1, r2, r3);
    }
    public static (T1, T2, T3, T4) ReadTuple<T1, T2, T3, T4>()
    {
        var r = RStrings();
        var r1 = (T1)Convert.ChangeType(r[0], typeof(T1));
        var r2 = (T2)Convert.ChangeType(r[1], typeof(T2));
        var r3 = (T3)Convert.ChangeType(r[2], typeof(T3));
        var r4 = (T4)Convert.ChangeType(r[3], typeof(T4));
        return (r1, r2, r3, r4);
    }
}


Measured memory_bytes: 46232