import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.NoSuchElementException;

public class Main implements Runnable {
    public static void main(String[] args) {
        new Thread(null,new Main(), "" ,Runtime.getRuntime().maxMemory()).start();
    }

    public void run() {
        FastScanner sc = new FastScanner();
        int n = sc.nextInt();
        char[] s = sc.next().toCharArray();
        int[][] sum = new int[3][n + 1];
        for(int i = 1;i < n + 1;i++) {
            int r = 0;
            int g = 0;
            int b = 0;
            if(s[i - 1] == 'R') r++;
            else if(s[i - 1] == 'G') g++;
            else b++;
            sum[0][i] = sum[0][i - 1] + r;
            sum[1][i] = sum[1][i - 1] + g;
            sum[2][i] = sum[2][i - 1] + b;
        }
        
        long ans = 0;
        for(int i = 0;i < s.length - 2;i++) {
            for(int j = i + 1;j < s.length - 1;j++) {
                if(s[i] == s[j]) continue;
                if((s[i] == 'R' && s[j] == 'B') || (s[i] == 'B' && s[j] == 'R')) {
                    // Gの個数を調べる
                    long numG = sum[1][s.length] - sum[1][j + 1];
                    int checkIdx = j + j - i;
                    if(checkIdx < s.length && s[checkIdx] == 'G') numG--;
                    ans += numG;
                }
                else if((s[i] == 'R' && s[j] == 'G') || (s[i] == 'G' && s[j] == 'R')) {
                    // Bの個数を調べる
                    long numB = sum[2][s.length] - sum[2][j + 1];
                    int checkIdx = j + j - i;
                    if(checkIdx < s.length && s[checkIdx] == 'B') numB--;
                    ans += numB;
                }
                else {
                    // Rの個数を調べる
                    long numR = sum[0][s.length] - sum[0][j + 1];
                    int checkIdx = j + j - i;
                    if(checkIdx < s.length && s[checkIdx] == 'R') numR--;
                    ans += numR;
                }
            }
        }

        PrintWriter out =  new PrintWriter(System.out);
        out.println(ans);
        out.flush();
    }
}

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: 33648