using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using static System.Math;
using System.Text;
using System.Threading;
using System.Globalization;
using System.Runtime.CompilerServices;
using Library;

namespace Program
{
    public static class ABC162D
    {
        static public int numberOfRandomCases = 0;
        static public void MakeTestCase(List<string> _input, List<string> _output, ref Func<string[], bool> _outputChecker)
        {
        }
        static public void Solve()
        {
            var N = NN;
            var S = NS;
            var segr = new LIB_SegTree<long>(N, 0, (x, y) => x + y);
            var segg = new LIB_SegTree<long>(N, 0, (x, y) => x + y);
            var segb = new LIB_SegTree<long>(N, 0, (x, y) => x + y);
            for (var i = 0; i < N; i++)
            {
                if (S[i] == 'R') segr[i] = 1;
                else if (S[i] == 'G') segg[i] = 1;
                else segb[i] = 1;
            }
            var ans = 0L;
            for (var i = 0; i < N; i++)
            {
                for (var j = i + 1; j < N; j++)
                {
                    var dif = j - i;
                    if (S[i] != S[j] && j + 1 <= N)
                    {
                        var tgt = 'G';
                        if (S[i] == 'R' && S[j] == 'G') tgt = 'B';
                        else if (S[i] == 'R' && S[j] == 'B') tgt = 'G';
                        else if (S[i] == 'G' && S[j] == 'R') tgt = 'B';
                        else if (S[i] == 'G' && S[j] == 'B') tgt = 'R';
                        else if (S[i] == 'B' && S[j] == 'R') tgt = 'G';
                        else tgt = 'R';
                        LIB_SegTree<long> seg;
                        if (tgt == 'R')
                        {
                            seg = segr;
                        }
                        else if (tgt == 'G')
                        {
                            seg = segg;
                        }
                        else
                        {
                            seg = segb;
                        }
                        if (j + dif < N)
                        {
                            var tmp = seg[j + dif];
                            seg[j + dif] = 0;
                            ans += seg.Query(j + 1, N);
                            seg[j + dif] = tmp;
                        }
                        else
                        {
                            ans += seg.Query(j + 1, N);
                        }
                    }
                }
            }
            Console.WriteLine(ans);
        }
        class Printer : StreamWriter
        {
            public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
            public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true)) { base.AutoFlush = false; }
            public Printer(Stream stream, Encoding encoding) : base(stream, encoding) { base.AutoFlush = false; }
        }
        static LIB_FastIO fastio = new LIB_FastIODebug();
        static public void Main(string[] args) { if (args.Length == 0) { fastio = new LIB_FastIO(); Console.SetOut(new Printer(Console.OpenStandardOutput())); } var t = new Thread(Solve, 134217728); t.Start(); t.Join(); Console.Out.Flush(); }
        static long NN => fastio.Long();
        static double ND => fastio.Double();
        static string NS => fastio.Scan();
        static long[] NNList(long N) => Repeat(0, N).Select(_ => NN).ToArray();
        static double[] NDList(long N) => Repeat(0, N).Select(_ => ND).ToArray();
        static string[] NSList(long N) => Repeat(0, N).Select(_ => NS).ToArray();
        static long Count<T>(this IEnumerable<T> x, Func<T, bool> pred) => Enumerable.Count(x, pred);
        static IEnumerable<T> Repeat<T>(T v, long n) => Enumerable.Repeat<T>(v, (int)n);
        static IEnumerable<int> Range(long s, long c) => Enumerable.Range((int)s, (int)c);
        static IOrderedEnumerable<T> OrderByRand<T>(this IEnumerable<T> x) => Enumerable.OrderBy(x, _ => xorshift);
        static IOrderedEnumerable<T> OrderBy<T>(this IEnumerable<T> x) => Enumerable.OrderBy(x.OrderByRand(), e => e);
        static IOrderedEnumerable<T1> OrderBy<T1, T2>(this IEnumerable<T1> x, Func<T1, T2> selector) => Enumerable.OrderBy(x.OrderByRand(), selector);
        static IOrderedEnumerable<T> OrderByDescending<T>(this IEnumerable<T> x) => Enumerable.OrderByDescending(x.OrderByRand(), e => e);
        static IOrderedEnumerable<T1> OrderByDescending<T1, T2>(this IEnumerable<T1> x, Func<T1, T2> selector) => Enumerable.OrderByDescending(x.OrderByRand(), selector);
        static IOrderedEnumerable<string> OrderBy(this IEnumerable<string> x) => x.OrderByRand().OrderBy(e => e, StringComparer.OrdinalIgnoreCase);
        static IOrderedEnumerable<T> OrderBy<T>(this IEnumerable<T> x, Func<T, string> selector) => x.OrderByRand().OrderBy(selector, StringComparer.OrdinalIgnoreCase);
        static IOrderedEnumerable<string> OrderByDescending(this IEnumerable<string> x) => x.OrderByRand().OrderByDescending(e => e, StringComparer.OrdinalIgnoreCase);
        static IOrderedEnumerable<T> OrderByDescending<T>(this IEnumerable<T> x, Func<T, string> selector) => x.OrderByRand().OrderByDescending(selector, StringComparer.OrdinalIgnoreCase);
        static uint xorshift { get { _xsi.MoveNext(); return _xsi.Current; } }
        static IEnumerator<uint> _xsi = _xsc();
        static IEnumerator<uint> _xsc() { uint x = 123456789, y = 362436069, z = 521288629, w = (uint)(DateTime.Now.Ticks & 0xffffffff); while (true) { var t = x ^ (x << 11); x = y; y = z; z = w; w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)); yield return w; } }
    }
}
namespace Library {
    class LIB_SegTree<T>
    {
        int n;
        T ti;
        Func<T, T, T> f;
        T[] dat;
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public LIB_SegTree(long _n, T _ti, Func<T, T, T> _f)
        {
            n = 1;
            while (n < _n) n <<= 1;
            ti = _ti;
            f = _f;
            dat = Enumerable.Repeat(ti, n << 1).ToArray();
            for (var i = n - 1; i > 0; i--) dat[i] = f(dat[(i << 1) | 0], dat[(i << 1) | 1]);
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public LIB_SegTree(IEnumerable<T> l, T _ti, Func<T, T, T> _f) : this(l.Count(), _ti, _f)
        {
            var idx = 0;
            foreach (var item in l) dat[n + idx++] = item;
            for (var i = n - 1; i > 0; i--) dat[i] = f(dat[(i << 1) | 0], dat[(i << 1) | 1]);
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Update(long i, T v)
        {
            dat[i += n] = v;
            while ((i >>= 1) > 0) dat[i] = f(dat[(i << 1) | 0], dat[(i << 1) | 1]);
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public T Query(long l, long r)
        {
            if (l == r) return ti;
            if (r < l) throw new Exception();
            var vl = ti;
            var vr = ti;
            for (long li = n + l, ri = n + r; li < ri; li >>= 1, ri >>= 1)
            {
                if ((li & 1) == 1) vl = f(vl, dat[li++]);
                if ((ri & 1) == 1) vr = f(dat[--ri], vr);
            }
            return f(vl, vr);
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        int FindToRight(int st, Func<T, bool> check, ref T acc, int k, int l, int r)
        {
            if (l + 1 == r)
            {
                acc = f(acc, dat[k]);
                return check(acc) ? k - n : -1;
            }
            int m = (l + r) >> 1;
            if (m <= st) return FindToRight(st, check, ref acc, (k << 1) | 1, m, r);
            if (st <= l && !check(f(acc, dat[k])))
            {
                acc = f(acc, dat[k]);
                return -1;
            }
            int vl = FindToRight(st, check, ref acc, (k << 1) | 0, l, m);
            if (vl != -1) return vl;
            return FindToRight(st, check, ref acc, (k << 1) | 1, m, r);
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public int FindToRight(int st, Func<T, bool> check)
        {
            T acc = ti;
            return FindToRight(st, check, ref acc, 1, 0, n);
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        int FindToLeft(int st, Func<T, bool> check, ref T acc, int k, int l, int r)
        {
            if (l + 1 == r)
            {
                acc = f(dat[k], acc);
                return check(acc) ? k - n : -1;
            }
            int m = (l + r) >> 1;
            if (m > st) return FindToLeft(st, check, ref acc, (k << 1) | 0, l, m);
            if (st >= r - 1 && !check(f(dat[k], acc)))
            {
                acc = f(dat[k], acc);
                return -1;
            }
            int vr = FindToLeft(st, check, ref acc, (k << 1) | 1, m, r);
            if (vr != -1) return vr;
            return FindToLeft(st, check, ref acc, (k << 1) | 0, l, m);
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public int FindToLeft(int st, Func<T, bool> check)
        {
            T acc = ti;
            return FindToLeft(st, check, ref acc, 1, 0, n);
        }
        public T this[long idx]
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            get { return dat[idx + n]; }
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            set { Update(idx, value); }
        }
    }
    class LIB_FastIO
    {
        public LIB_FastIO() { str = Console.OpenStandardInput(); }
        readonly Stream str;
        readonly byte[] buf = new byte[1024];
        int len, ptr;
        public bool isEof = false;
        public bool IsEndOfStream { get { return isEof; } }
        byte read()
        {
            if (isEof) throw new EndOfStreamException();
            if (ptr >= len)
            {
                ptr = 0;
                if ((len = str.Read(buf, 0, 1024)) <= 0)
                {
                    isEof = true;
                    return 0;
                }
            }
            return buf[ptr++];
        }
        char Char()
        {
            byte b = 0;
            do b = read();
            while (b < 33 || 126 < b);
            return (char)b;
        }
        virtual public string Scan()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)read())
                sb.Append(b);
            return sb.ToString();
        }
        virtual public long Long()
        {
            long ret = 0; byte b = 0; var ng = false;
            do b = read();
            while (b != '-' && (b < '0' || '9' < b));
            if (b == '-') { ng = true; b = read(); }
            for (; true; b = read())
            {
                if (b < '0' || '9' < b)
                    return ng ? -ret : ret;
                else ret = ret * 10 + b - '0';
            }
        }
        virtual public double Double() { return double.Parse(Scan(), CultureInfo.InvariantCulture); }
    }
    class LIB_FastIODebug : LIB_FastIO
    {
        Queue<string> param = new Queue<string>();
        string NextString() { if (param.Count == 0) foreach (var item in Console.ReadLine().Split(' ')) param.Enqueue(item); return param.Dequeue(); }
        public LIB_FastIODebug() { }
        public override string Scan() => NextString();
        public override long Long() => long.Parse(NextString());
        public override double Double() => double.Parse(NextString());
    }
}


Measured memory_bytes: 19220