using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;

namespace AtCorder
{
	public class Program
	{
		static void Main(string[] args)
		{
			var cin = new Scanner2();
			int n = cin.Int();
			string s = cin.Next();

			var ruiR = new int[n + 1];
			var ruiG = new int[n + 1];
			var ruiB = new int[n + 1];
			for (int i = 0; i < n; i++) {
				if (s[i] == 'R') {
					ruiR[i + 1] = ruiR[i] + 1;
					ruiG[i + 1] = ruiG[i];
					ruiB[i + 1] = ruiB[i];
				} else if (s[i] == 'G') {
					ruiR[i + 1] = ruiR[i];
					ruiG[i + 1] = ruiG[i] + 1;
					ruiB[i + 1] = ruiB[i];
				} else {
					ruiR[i + 1] = ruiR[i];
					ruiG[i + 1] = ruiG[i];
					ruiB[i + 1] = ruiB[i] + 1;
				}
			}

			long ans = 0;
			for (int i = 0; i < n; i++) {
				if (s[i] == 'R') {
					for (int j = i + 1; j < n; j++) {
						if (s[j] == 'G') {
							ans += ruiB[n] - ruiB[j + 1];
							if (j + (j - i) < n && s[j + (j - i)] == 'B') {
								ans -= 1;
							}
						} else if (s[j] == 'B') {
							ans += ruiG[n] - ruiG[j + 1];
							if (j + (j - i) < n && s[j + (j - i)] == 'G') {
								ans -= 1;
							}
						}
					}
				} else if (s[i] == 'G') {
					for (int j = i + 1; j < n; j++) {
						if (s[j] == 'R') {
							ans += ruiB[n] - ruiB[j + 1];
							if (j + (j - i) < n && s[j + (j - i)] == 'B') {
								ans -= 1;
							}
						} else if (s[j] == 'B') {
							ans += ruiR[n] - ruiR[j + 1];
							if (j + (j - i) < n && s[j + (j - i)] == 'R') {
								ans -= 1;
							}
						}
					}
				} else {
					for (int j = i + 1; j < n; j++) {
						if (s[j] == 'R') {
							ans += ruiG[n] - ruiG[j + 1];
							if (j + (j - i) < n && s[j + (j - i)] == 'G') {
								ans -= 1;
							}
						} else if (s[j] == 'G') {
							ans += ruiR[n] - ruiR[j + 1];
							if (j + (j - i) < n && s[j + (j - i)] == 'R') {
								ans -= 1;
							}
						}
					}
				}
			}

			Console.WriteLine(ans);
		}

	}

	public static class Helper
	{
		public static void UpdateMin32<T>(T array, int index, int value) where T : IList<int>
			=> array[index] = Math.Min(array[index], value);
		public static void UpdateMax32<T>(T array, int index, int value) where T : IList<int>
			=> array[index] = Math.Max(array[index], value);
		public static void UpdateMin64<T>(T array, int index, long value) where T : IList<long>
			=> array[index] = Math.Min(array[index], value);
		public static void UpdateMax64<T>(T array, int index, long value) where T : IList<long>
			=> array[index] = Math.Max(array[index], value);

		public static T[] Array<T>(int n, Func<int, T> init)
			=> Enumerable.Range(0, n).Select(x => init(x)).ToArray();
		public static List<T> List<T>(int n, Func<int, T> init)
			=> Enumerable.Range(0, n).Select(x => init(x)).ToList();

		private static readonly int[] delta4_ = { 1, 0, -1, 0, 1 };
		public static void DoAt4(int i, int j, int imax, int jmax, Action<int, int> action)
		{
			for (int n = 0; n < 4; n++) {
				int ii = i + delta4_[n];
				int jj = j + delta4_[n + 1];
				if ((uint)ii < (uint)imax && (uint)jj < (uint)jmax) {
					action(ii, jj);
				}
			}
		}
	}

	public class Scanner2
	{
		private readonly char[] delimiter_ = new char[] { ' ' };
		private readonly string filePath_;
		private readonly Func<string> reader_;
		private string[] buf_;
		private int index_;

		public Scanner2(string file = "")
		{
			if (string.IsNullOrWhiteSpace(file)) {
				reader_ = Console.ReadLine;
			} else {
				filePath_ = file;
				var fs = new StreamReader(file);
				reader_ = fs.ReadLine;
			}
			buf_ = new string[0];
			index_ = 0;
		}

		public string Next()
		{
			if (index_ < buf_.Length) {
				return buf_[index_++];
			}

			string st = reader_();
			while (st == "") {
				st = reader_();
			}

			buf_ = st.Split(delimiter_, StringSplitOptions.RemoveEmptyEntries);
			if (buf_.Length == 0) {
				return Next();
			}

			index_ = 0;
			return buf_[index_++];
		}

		public int Int() => int.Parse(Next());
		public long Long() => long.Parse(Next());
		public double Double() => double.Parse(Next());

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

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

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

		public void Save(string text)
		{
			if (string.IsNullOrWhiteSpace(filePath_)) {
				return;
			}

			File.WriteAllText(filePath_ + "_output.txt", text);
		}
	}
}

Measured memory_bytes: 27624