using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Linq;
using System.Numerics;

namespace AtCoderWorkspace
{
    public class Solver
    {
        public void Solve()
        {
            var cin = new Scanner();            
            var n = cin.nextInt();
            var s = cin.next().ToCharArray();

            var Rcount = new long[n+1];
            var Gcount = new long[n+1];
            var Bcount = new long[n+1];
            Rcount[0] = 0;
            Gcount[0] = 0;
            Bcount[0] = 0;
            for (int i = 1; i <= n; i++)
            {
                if (s[i-1] == 'R') Rcount[i] = Rcount[i - 1] + 1;
                else Rcount[i] = Rcount[i - 1];
                if (s[i-1] == 'G') Gcount[i] = Gcount[i - 1] + 1;
                else Gcount[i] = Gcount[i - 1];
                if (s[i-1] == 'B') Bcount[i] = Bcount[i - 1] + 1;
                else Bcount[i] = Bcount[i - 1];
            }

            var ans = 0L;
            for (int i = 0; i < n; i++)
            {                
                var a = s[i];                
                for (int j = i+1; j < n; j++)
                {
                    var bex = s[j];
                    if (bex != a)
                    {
                        var b = bex;
                        var dis1 = j - i;

                        var contena = new HashSet<char>();
                        contena.Add(a);
                        contena.Add(b);

                        //j+1からnまでのcの個数は？
                        if(!contena.Contains('B'))
                        {
                            var bc = Bcount[n] - Bcount[j + 1];
                            if (s.Count() > j+dis1 && s[j + dis1] == 'B' && bc != 0)
                                bc--;
                            ans += bc;
                            continue;
                        }
                        if (!contena.Contains('G'))
                        {
                            var gc = Gcount[n] - Gcount[j + 1];
                            if (s.Count() > j + dis1 && s[j + dis1] == 'G' && gc != 0)
                                gc--;
                            ans += gc;
                        }
                        if (!contena.Contains('R'))
                        {
                            var rc = Rcount[n] - Rcount[j + 1];
                            if (s.Count() > j + dis1 && s[j + dis1] == 'R' && rc != 0)
                                rc--;
                            ans += rc;
                            continue;
                        }
                    }
                }
            }

            Console.WriteLine(ans);
        }

    }

    class Scanner
    {
        string[] s;
        int i;

        char[] cs = new char[] { ' ' };

        public Scanner()
        {
            s = new string[0];
            i = 0;
        }

        public string next()
        {
            if (i < s.Length) return s[i++];
            string st = Console.ReadLine();
            while (st == "") st = Console.ReadLine();
            s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
            if (s.Length == 0) return next();
            i = 0;
            return s[i++];
        }

        public int nextInt()
        {
            return int.Parse(next());
        }
        public int[] ArrayInt(int N, int add = 0)
        {
            int[] Array = new int[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextInt() + add;
            }
            return Array;
        }

        public int[] DPArrayInt(int N, int ex)
        {
            int[] Array = new int[N + ex];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextInt();
            }
            return Array;
        }

        public long nextLong()
        {
            return long.Parse(next());
        }

        public long[] ArrayLong(int N, long add = 0)
        {
            long[] Array = new long[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextLong() + add;
            }
            return Array;
        }

        public long[] DPArrayLong(int N, int ex)
        {
            long[] Array = new long[N + ex];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextLong();
            }
            return Array;
        }

        public double nextDouble()
        {
            return double.Parse(next());
        }


        public double[] ArrayDouble(int N, double add = 0)
        {
            double[] Array = new double[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextDouble() + add;
            }
            return Array;
        }
    }

    class Program
    {
        static void Main(string[] s) => new Solver().Solve();
    }
}


Measured memory_bytes: 41368