import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.InputMismatchException;
import java.io.IOException;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Sparsh Sanchorawala
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        DRGBTriplets solver = new DRGBTriplets();
        solver.solve(1, in, out);
        out.close();
    }

    static class DRGBTriplets {
        public void solve(int testNumber, InputReader s, PrintWriter w) {
            int n = s.nextInt();
            String str = s.next();
            int[] a = new int[n];
            for (int i = 0; i < n; i++) {
                if (str.charAt(i) == 'R')
                    a[i] = 0;
                else if (str.charAt(i) == 'G')
                    a[i] = 1;
                else
                    a[i] = 2;
            }
            long[] f = new long[3];
            for (int i = 0; i < n; i++)
                f[a[i]]++;
            long res = f[0] * f[1] * f[2];
            for (int i = 0; i < n; i++) {
                for (int j = 1; i - j >= 0 && i + j < n; j++) {
                    int[] c = new int[3];
                    c[a[i - j]] = 1;
                    c[a[i]] = 1;
                    c[a[i + j]] = 1;
                    int ck = 1;
                    for (int z = 0; z < 3; z++)
                        if (c[z] == 0)
                            ck = 0;
                    res -= ck;
                }
            }
            w.println(res);
        }

    }

    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private InputReader.SpaceCharFilter filter;

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        public int read() {
            if (numChars == -1) {
                throw new InputMismatchException();
            }
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (numChars <= 0) {
                    return -1;
                }
            }
            return buf[curChar++];
        }

        public int nextInt() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public String nextString() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            StringBuilder res = new StringBuilder();
            do {
                if (Character.isValidCodePoint(c)) {
                    res.appendCodePoint(c);
                }
                c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }

        public boolean isSpaceChar(int c) {
            if (filter != null) {
                return filter.isSpaceChar(c);
            }
            return isWhitespace(c);
        }

        public static boolean isWhitespace(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public String next() {
            return nextString();
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);

        }

    }
}



Measured memory_bytes: 49644