import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.TreeSet;
import java.util.function.DoubleUnaryOperator;
import java.util.function.IntUnaryOperator;
import java.util.function.LongUnaryOperator;


public class Main {
    public static void main(String[] args) {
        StringBuilder out = new StringBuilder();
        solve(out);
        PrintWriter pw = new PrintWriter(System.out);
        pw.println(out);
        pw.flush();
        pw.close();
    }

    public static void solve(StringBuilder out) {
        int n = In.ni();
        char[] s = In.nc();
        long ans = MathUtil.comb(n, 3);
        long[] r = new long[n + 1];
        long[] g = new long[n + 1];
        long[] b = new long[n + 1];
        for (int i = 1; i <= n; i++) {
            if (s[i - 1] == 'R') {
                r[i]++;
            } else if (s[i - 1] == 'G') {
                g[i]++;
            } else {
                b[i]++;
            }
            r[i] += r[i - 1];
            g[i] += g[i - 1];
            b[i] += b[i - 1];
        }
        long sub = 0;
        for (int j = 0; j < n; j++) {
            sub += Math.min(j, n - j - 1);
        }
        sub += MathUtil.comb(r[n], 3);
        sub += MathUtil.comb(g[n], 3);
        sub += MathUtil.comb(b[n], 3);
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                if (s[i] == s[j]) {
                    if (s[i] == 'R') {
                        sub += g[n] - g[j + 1];
                        sub += b[n] - b[j + 1];
                    } else if (s[i] == 'G') {
                        sub += b[n] - b[j + 1];
                        sub += r[n] - r[j + 1];
                    } else {
                        sub += r[n] - r[j + 1];
                        sub += g[n] - g[j + 1];
                    }
                }
            }
        }
        for (int j = 0; j < n; j++) {
            for (int k = j + 1; k < n; k++) {
                if (s[j] == s[k]) {
                    if (s[j] == 'R') {
                        sub += g[j];
                        sub += b[j];
                    } else if (s[j] == 'G') {
                        sub += b[j];
                        sub += r[j];
                    } else {
                        sub += r[j];
                        sub += g[j];
                    }
                }
            }
        }
        for (int i = 0; i < n; i++) {
            for (int k = i + 2; k < n; k++) {
                if (s[i] == s[k]) {
                    if (s[k] == 'R') {
                        sub += g[k] - g[i + 1];
                        sub += b[k] - b[i + 1];
                    } else if (s[k] == 'G') {
                        sub += b[k] - b[i + 1];
                        sub += r[k] - r[i + 1];
                    } else {
                        sub += r[k] - r[i + 1];
                        sub += g[k] - g[i + 1];
                    }
                }
            }
        }
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                int k = j + (j - i);
                boolean bij = s[i] == s[j];
                if (k < n) {
                    boolean bjk = s[j] == s[k];
                    boolean bik = s[i] == s[k];
                    if (bij && bjk) {
                        sub--;
                    } else if (bij && !bjk || bjk && !bik || bik && !bij) {
                        sub--;
                    }
                }
            }
        }
        out.append(ans - sub);
    }
}


/**
 * @author https://atcoder.jp/users/suisen
 */
class In {
    public static final FastScanner fsc = new FastScanner();

    public static int ni() {
        return fsc.nextInt();
    }

    public static int ni(IntUnaryOperator f) {
        return f.applyAsInt(fsc.nextInt());
    }

    public static int[] ni(int n) {
        int[] a = new int[n];
        Arrays.setAll(a, i -> fsc.nextInt());
        return a;
    }

    public static int[] ni (int n, IntUnaryOperator f) {
        int[] a = new int[n];
        Arrays.setAll(a, i -> ni(f));
        return a;
    }

    public static int[][] ni(int n, int m) {
        int[][] a = new int[n][m];
        Arrays.setAll(a, i -> ni(m));
        return a;
    }

    public static int[][] ni(int n, int m, IntUnaryOperator f) {
        int[][] a = new int[n][m];
        Arrays.setAll(a, i -> ni(m, f));
        return a;
    }

    public static long nl() {
        return fsc.nextLong();
    }

    public static long nl(LongUnaryOperator f) {
        return f.applyAsLong(fsc.nextLong());
    }

    public static long[] nl(int n) {
        long[] a = new long[n];
        Arrays.setAll(a, i -> fsc.nextLong());
        return a;
    }

    public static long[] nl(int n, LongUnaryOperator f) {
        long[] a = new long[n];
        Arrays.setAll(a, i -> nl(f));
        return a;
    }

    public static long[][] nl(int n, int m) {
        long[][] a = new long[n][m];
        Arrays.setAll(a, i -> nl(m));
        return a;
    }

    public static long[][] nl(int n, int m, LongUnaryOperator f) {
        long[][] a = new long[n][m];
        Arrays.setAll(a, i -> nl(m, f));
        return a;
    }

    public static char[] nc() {
        return fsc.next().toCharArray();
    }

    public static char[][] nc(int n, int m) {
        char[][] c = new char[n][m];
        Arrays.setAll(c, i -> nc());
        return c;
    }

    public static double nd() {
        return fsc.nextDouble();
    }

    public static double nd(DoubleUnaryOperator f) {
        return f.applyAsDouble(fsc.nextDouble());
    }

    public static double[] nd(int n) {
        double[] a = new double[n];
        Arrays.setAll(a, i -> fsc.nextDouble());
        return a;
    }

    public static double[] nd(int n, DoubleUnaryOperator f) {
        double[] a = new double[n];
        Arrays.setAll(a, i -> nd(f));
        return a;
    }

    public static double[][] nd(int n, int m) {
        double[][] a = new double[n][m];
        Arrays.setAll(a, i -> nd(m));
        return a;
    }

    public static double[][] nd(int n, int m, DoubleUnaryOperator f) {
        double[][] a = new double[n][m];
        Arrays.setAll(a, i -> nd(m, f));
        return a;
    }

    public static String ns() {
        return fsc.next();
    }

    public static String[] ns(int n) {
        String[] s = new String[n];
        Arrays.setAll(s, i -> ns());
        return s;
    }

    public static boolean[][] grid(int h, int w, char trueCharacter) {
        boolean[][] grid = new boolean[h][w];
        for (int i = 0; i < h; i++) {
            char[] s = fsc.next().toCharArray();
            for (int j = 0; j < w; j++) {
                grid[i][j] = s[j] == trueCharacter;
            }
        }
        return grid;
    }
}


class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;

    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        } else {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }

    private int readByte() {
        if (hasNextByte()) {
            return buffer[ptr++];
        } else {
            return -1;
        }
    }

    private static boolean isPrintableChar(int c) {
        return 33 <= c && c <= 126;
    }

    public boolean hasNext() {
        while (hasNextByte() && !isPrintableChar(buffer[ptr])) {
            ptr++;
        }
        return hasNextByte();
    }

    public String next() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    public long nextLong() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while (true) {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }

    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) {
            throw new NumberFormatException();
        }
        return (int) nl;
    }

    public double nextDouble() {
        return Double.parseDouble(next());
    }
}


/**
 * @author https://atcoder.jp/users/suisen
 */
class MathUtil{
    private static final long UNDER32_MASK = 0xffff_ffffl;

    private MathUtil(){}
    
    /**
     * Enumarate primes equal to or less than n.
     * @param n
     * @return {@code ArrayList} that holds primes.
     */
    public static ArrayList<Integer> eratosthenes(int n) {
        int[] div = eratosthenesDivisors(n);
        ArrayList<Integer> result = new ArrayList<>();
        for (int i = 2; i <= n; i++) if (div[i] == i) result.add(i);
        return result;
    }

    /**
     * execute eratosthenes's prime-enumerate algorithm. a[i] holds the greatest
     * divisor of i. if a[i] = i, i is a prime number. This arrary enables you to
     * prime-factorize in O(log n) time.
     * @param n
     * @return divisor array.
     */
    public static int[] eratosthenesDivisors(int n) {
        int[] divisors = new int[n + 1];
        if (n <= 0) return null;
        for (int i = 1; i <= n; i++) {
            if ((i & 1) != 0) divisors[i] = i;
            else divisors[i] = 2;
        }
        for (int i = 3; i <= n; i += 2) {
            if (divisors[i] == i) {
                for (long j = (long) i * i; j <= n; j += i << 1) {
                    divisors[(int) j] = i;
                }
            }
        }
        return divisors;
    }

    /**
     * Caluculate prime-factorization in O(sqrt(n)) time.
     * @param n
     * @return {@code HashMap} of {prime: index}
     */
    public static HashMap<Long, Integer> primeFactorization(long n) {
        HashMap<Long, Integer> primes = new HashMap<>();
        for (long p = 2; p * p <= n; p++) {
            int q = 0;
            while (n % p == 0) {
                n /= p;
                q++;
            }
            if (q > 0) primes.put(p, q);
        }
        if (n > 1) primes.put(n, 1);
        return primes;
    }

    public static TreeSet<Long> divisors(long n) {
        TreeSet<Long> divisors = new TreeSet<>();
        for (long i = 1; i * i <= n; i++) {
            if (n % i == 0) {
                divisors.add(i);
                divisors.add(n / i);
            }
        }
        return divisors;
    }

    private static HashMap<Long, Integer> lcmMap(HashMap<Long, Integer> amap, HashMap<Long, Integer> bmap) {
        if (amap.size() < bmap.size()) return lcmMap(bmap, amap);
        HashMap<Long, Integer> lcm = amap;
        for (Map.Entry<Long, Integer> e : bmap.entrySet()) {
            long prime = e.getKey();
            if (lcm.containsKey(prime)) lcm.put(prime, Math.max(lcm.get(prime), e.getValue()));
            else lcm.put(prime, e.getValue());
        }
        return lcm;
    }

    private static HashMap<Long, Integer> lcmMap(HashMap<Long, Integer> amap, long b) {
        HashMap<Long, Integer> bmap = primeFactorization(b);
        return lcmMap(amap, bmap);
    }

    public static HashMap<Long, Integer> lcmMap(long... a) {
        HashMap<Long, Integer> amap = new HashMap<>();
        for (long c : a) amap = lcmMap(amap, c);
        return amap;
    }

    /**
     * calculate lcm(a, b) fast. (NOT considering overflow.)
     */
    public static long lcm(long a, long b) {
        return (a / gcd(a, b)) * b;
    }

    /**
     * Caluculate the GCD of (a, b)/
     * 
     * @param a first value
     * @param b second value
     * @return GCD(a, b)
     */
    public static long gcd(long a, long b) {
        if (a < b) return gcd(b, a);
        if (b == 0) return a;
        if (a == 0) return b;
        long r = a % b;
        while (r != 0) {
            a = b;
            b = r;
            r = a % b;
        }
        return b;
    }

    public static long gcd(long... a){
        long gcd = 0;
        for (long c : a) gcd = gcd(gcd, c);
        return gcd;
    }

    /**
     * Return one of the solutions to {@code ax+by=gcd(a, b)}.
     * @return {@code x}, {@code y}, {@code gcd(a, b)}.
     * @param a a of ax+by=gcd(a, b).
     * @param b b of ax+by=gcd(a, b). class ReferenceLong is a reference type of long.
     */
    public static long[] extGCD(long a, long b) {
        long[] ret = new long[3];
        long[] xy = new long[2];
        ret[2] = extGCD(a, b, xy);
        ret[0] = xy[0];
        ret[1] = xy[1];
        return ret;
    }

    private static long extGCD(long a, long b, long[] xy) {
        if (b == 0) {
            xy[0] = 1;
            xy[1] = 0;
            return a;
        }
        long tmp = xy[0];
        xy[0] = xy[1];
        xy[1] = tmp;
        long d = extGCD(b, a % b, xy);
        xy[1] -= a / b * xy[0];
        return d;
    }
    
    /**
     * caluculate a ^ b NOT considering overflow.
     * so if you want to calculate a ^ b (mod p), use ModUtil.pow(a, b).
     * @param a base
     * @param b exponent
     * @return a ^ b
     */
    public static long pow(int a, long b) {
        long ret = 1l;
        for (long c = 1, ac = a; b > 0; ac *= ac, c <<= 1) {
            if ((-b & b) == c) {
                ret *= ac;
                b &= ~(-b & b);
            }
        }
        return ret;
    }

    /**
     * Caluculate the combination nCr NOT considering overflow.
     * 
     * @param n left
     * @param r right
     * @return nCr
     */
    public static long comb(long n, long r) {
        if (n < r) return 0;
        r = Math.min(r, n - r);
        long res = 1;
        for (long d = 1; d <= r; d++) {
            res *= n--;
            res /= d;
        }
        return res;
    }

    public static long ceilSqrt(long n) {
        long l = -1;
        long r = n;
        while (r - l > 1) {
            long m = (r + l) >> 1;
            if (m * m >= n) {
                r = m;
            } else {
                l = m;
            }
        }
        return r;
    }

    public static long floorSqrt(long n) {
        long l = 0;
        long r = n + 1;
        while (r - l > 1) {
            long m = (r + l) >> 1;
            if (m * m > n) {
                r = m;
            } else {
                l = m;
            }
        }
        return l;
    }

    public static long int2ToLong(int upper, int lower) {
        return ((long) upper << Integer.SIZE) | lower;
    }

    public static int upper32(long l) {
        return (int) (l >>> Integer.SIZE);
    }

    public static int lower32(long l) {
        return (int) (l & UNDER32_MASK);
    }
}


Measured memory_bytes: 36360