import java.io.*;
import java.math.BigInteger;
import java.util.*;

 class Main {

	static long sx = 0, sy = 0, mod = (long) (1e9 + 7);

	static ArrayList<Integer>[] a;
	static long[][] dp;
	static long[] fa;
	static long[] farr;
	public static PrintWriter out;
	static ArrayList<pair> pa = new ArrayList<>();
	static long[] fact = new long[(int) 1e6];
	static boolean b = false;
	static StringBuilder sb = new StringBuilder();
	static boolean cycle = false;
	// static long m = 998244353;
	static long[] no, col;
	static String s;
	static int k = 0, n = 0, m = 0;
	static int[] c;
	static long ans = 0;
	static HashMap<Integer, Integer> hm;
	// static ArrayList<Integer> p = new ArrayList<>();
	static long[] arr;;
	static long[] p;

	public static void main(String[] args) throws IOException {

		Scanner scn = new Scanner(new BufferedReader(new InputStreamReader(System.in)));

		out = new PrintWriter(System.out);
		// Reader scn = new Reader();

		int n = scn.nextInt();

		String s = scn.next();

		int[] r = new int[n];
		int[] g = new int[n];
		int[] b = new int[n];

		if (s.charAt(n - 1) == 'R')
			r[n - 1] = 1;

		else if (s.charAt(n - 1) == 'G')
			g[n - 1] = 1;
		else
			b[n - 1] = 1;

		for (int i = n - 2; i >= 0; i--) {

			r[i] += r[i + 1];
			g[i] += g[i + 1];
			b[i] += b[i + 1];

			if (s.charAt(i) == 'R')
				r[i]++;
			else if (s.charAt(i) == 'G')
				g[i]++;
			else
				b[i]++;
		}

		long ans = 0;

		for (int i = 0; i <= n - 3; i++) {

			for (int j = i + 1; j <= n - 2; j++) {

				int d = j - i;
				
				 HashSet<Character>hm = new HashSet<>();
				 
				 hm.add(s.charAt(i));
				 hm.add(s.charAt(j));

				if (hm.contains('R') && hm.contains('G')) {

					ans += b[j + 1];

					if (j + d < n && s.charAt(j + d) == 'B')
						ans--;
				}

				else if (hm.contains('R') && hm.contains('B')) {
					ans += g[j + 1];

					if (j + d < n && s.charAt(j + d) == 'G')
						ans--;
				}

				else if(hm.contains('B') && hm.contains('G')){
					ans += r[j + 1];

					if (j + d < n && s.charAt(j + d) == 'R')
						ans--;
				}
			}
		}

		System.out.println(ans);
	}

	// _________________________TEMPLATE_____________________________________________________________

	// public static long lcm(long x, long y) {
	//
	// return (x * y) / gcd(x, y);
	// }
	//
	private static long gcd(long x, long y) {
		if (x == 0)
			return y;

		return gcd(y % x, x);
	}
	//
	// static class comp implements Comparator<pair> {
	//
	// @Override
	// public int compare(pair p1, pair p2) {
	// return p1.i - p2.i;
	// }
	//
	// }
	//
	// public static long pow(long a, long b) {
	//
	// if (b < 0)
	// return 0;
	// if (b == 0 || b == 1)
	// return (long) Math.pow(a, b);
	//
	// if (b % 2 == 0) {
	//
	// long ret = pow(a, b / 2);
	// ret = (ret % mod * ret % mod) % mod;
	// return ret;
	// }
	//
	// else {
	// return ((pow(a, b - 1) % mod) * a % mod) % mod;
	// }
	// }

	private static class pair implements Comparable<pair> {

		long no;
		long s, e;

		pair(long n, long c, long d) {
			no = n;
			s = c;
			e = d;

		}

		@Override
		public int compareTo(pair o) {

			return 1;

		}

		// @Override
		//
		// public int hashCode() {
		// return i;
		// }
		//
		// @Override
		//
		// public boolean equals(Object o) {
		//
		// pair p = (pair) o;
		// return this.i == p.i;
		// }

	}

	private static String reverse(String s) {

		return new StringBuilder(s).reverse().toString();
	}

	public static class Reader {
		final private int BUFFER_SIZE = 1 << 16;
		private DataInputStream din;
		private byte[] buffer;
		private int bufferPointer, bytesRead;

		public Reader() {
			din = new DataInputStream(System.in);
			buffer = new byte[BUFFER_SIZE];
			bufferPointer = bytesRead = 0;
		}

		public Reader(String file_name) throws IOException {
			din = new DataInputStream(new FileInputStream(file_name));
			buffer = new byte[BUFFER_SIZE];
			bufferPointer = bytesRead = 0;
		}

		public String readLine() throws IOException {
			byte[] buf = new byte[1000000 + 1]; // line length
			int cnt = 0, c;
			while ((c = read()) != -1) {
				if (c == '\n')
					break;
				buf[cnt++] = (byte) c;
			}
			return new String(buf, 0, cnt);
		}

		public int nextInt() throws IOException {
			int ret = 0;
			byte c = read();
			while (c <= ' ')
				c = read();
			boolean neg = (c == '-');
			if (neg)
				c = read();
			do {
				ret = ret * 10 + c - '0';
			} while ((c = read()) >= '0' && c <= '9');

			if (neg)
				return -ret;
			return ret;
		}

		public long nextLong() throws IOException {
			long ret = 0;
			byte c = read();
			while (c <= ' ')
				c = read();
			boolean neg = (c == '-');
			if (neg)
				c = read();
			do {
				ret = ret * 10 + c - '0';
			} while ((c = read()) >= '0' && c <= '9');
			if (neg)
				return -ret;
			return ret;
		}

		public double nextDouble() throws IOException {
			double ret = 0, div = 1;
			byte c = read();
			while (c <= ' ')
				c = read();
			boolean neg = (c == '-');
			if (neg)
				c = read();

			do {
				ret = ret * 10 + c - '0';
			} while ((c = read()) >= '0' && c <= '9');

			if (c == '.') {
				while ((c = read()) >= '0' && c <= '9') {
					ret += (c - '0') / (div *= 10);
				}
			}

			if (neg)
				return -ret;
			return ret;
		}

		private void fillBuffer() throws IOException {
			bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
			if (bytesRead == -1)
				buffer[0] = -1;
		}

		private byte read() throws IOException {
			if (bufferPointer == bytesRead)
				fillBuffer();
			return buffer[bufferPointer++];
		}

		public void close() throws IOException {
			if (din == null)
				return;
			din.close();
		}

		public int[] nextIntArray(int n) throws IOException {
			int[] arr = new int[n];
			for (int i = 0; i < n; i++) {
				arr[i] = nextInt();
			}
			return arr;
		}

		public long[] nextLongArray(int n) throws IOException {
			long[] arr = new long[n];
			for (int i = 0; i < n; i++) {
				arr[i] = nextLong();
			}
			return arr;
		}

		public int[][] nextInt2DArray(int m, int n) throws IOException {
			int[][] arr = new int[m][n];
			for (int i = 0; i < m; i++) {
				for (int j = 0; j < n; j++)
					arr[i][j] = nextInt();
			}
			return arr;
		}

		public long[][] nextInt2DArrayL(int m, int n) throws IOException {
			long[][] arr = new long[m][n];
			for (int i = 0; i < m; i++) {
				for (int j = 0; j < n; j++)
					arr[i][j] = nextInt();
			}
			return arr;
		}
		// kickstart - Solution
		// atcoder - Main
	}

}

Measured memory_bytes: 68896