import java.util.*;
import java.io.*;

public class Main {

    public static void main(String[] args) {
        FastScanner sc = new FastScanner();
        int n = sc.nextInt();
        int[] rgb = new int[n];
        int[] rsum = new int[n+1];
        int[] gsum = new int[n+1];
        int[] bsum = new int[n+1];
        String s = sc.next();
        for (int i = 0; i < s.length(); i++) {
            rsum[i+1] = rsum[i];
            gsum[i+1] = gsum[i];
            bsum[i+1] = bsum[i];
            if(s.charAt(i) == 'R'){
                rsum[i+1]++;
                rgb[i] = 1;
            }else if(s.charAt(i) == 'G'){
                gsum[i+1]++;
                rgb[i] = 2;
            }else{
                bsum[i+1]++;
                rgb[i] = 3;
            }
        }

        long ans = 0;

        for (int i = 0; i < n; i++) {
            int ti = rgb[i];
            for (int j = i+1; j < n; j++) {
                int tj = rgb[j];
                if(ti == tj) continue;
                if(ti+tj == 3){
                    ans += bsum[n] - bsum[j];
                    if(j + (j-i) < n && rgb[j + (j-i)] == 3) ans--;
                }else if(ti+tj == 4){
                    ans += gsum[n] - gsum[j];
                    if(j + (j-i) < n && rgb[j + (j-i)] == 2) ans--;
                }else{
                    ans += rsum[n] - rsum[j];
                    if(j + (j-i) < n && rgb[j + (j-i)] == 1) ans--;
                }
            }
        }

        System.out.println(ans);
    
    }

    private static 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());}
    }
}



Measured memory_bytes: 33372