#![allow(unused_imports, unused_macros, dead_code)]

macro_rules! min {
    (.. $x:expr) => {{
        let mut it = $x.iter();
        it.next().map(|z| it.fold(z, |x, y| min!(x, y)))
    }};
    ($x:expr) => ($x);
    ($x:expr, $($ys:expr),*) => {{
        let t = min!($($ys),*);
        if $x < t { $x } else { t }
    }}
}
macro_rules! max {
    (.. $x:expr) => {{
        let mut it = $x.iter();
        it.next().map(|z| it.fold(z, |x, y| max!(x, y)))
    }};
    ($x:expr) => ($x);
    ($x:expr, $($ys:expr),*) => {{
        let t = max!($($ys),*);
        if $x > t { $x } else { t }
    }}
}
macro_rules! ewriteln {
    ($($args:expr),*) => { let _ = writeln!(&mut std::io::stderr(), $($args),*); };
}
macro_rules! trace {
    ($x:expr) => { ewriteln!(">>> {} = {:?}", stringify!($x), $x) };
    ($($xs:expr),*) => { trace!(($($xs),*)) }
}
macro_rules! put {
    (.. $x:expr) => {{
        let mut it = $x.iter();
        if let Some(x) = it.next() { print!("{}", x); }
        for x in it { print!(" {}", x); }
        println!("");
    }};
    ($x:expr) => { println!("{}", $x) };
    ($x:expr, $($xs:expr),*) => { print!("{} ", $x); put!($($xs),*) }
}

const M: i64 = 1_000_000_007;

fn char2int(a: char) -> u64 {
    (a as u8) as u64
}

fn int2char(x: u64) -> char {
    (x as u8) as char
}

fn nokori(a: char, b: char) -> char {
    let x = char2int('R') + char2int('G') + char2int('B') - char2int(a) - char2int(b);
    int2char(x)
}

fn count(begin: usize, end: usize, c: char, r: &Vec<usize>, g: &Vec<usize>, b: &Vec<usize>) -> usize {
    if c == 'R' {
        r[end] - r[begin]
    } else if c == 'G' {
        g[end] - g[begin]
    } else {
        b[end] - b[begin]
    }
}

fn main() {
    let mut sc = Scanner::new();
    let n: usize = sc.cin();
    let s: Vec<char> = sc.chars();

    let mut r: Vec<usize> = vec![0; n + 1];
    let mut g: Vec<usize> = vec![0; n + 1];
    let mut b: Vec<usize> = vec![0; n + 1];

    for i in 0..n {
        r[i + 1] = r[i] + if s[i] == 'R' { 1 } else { 0 };
        g[i + 1] = g[i] + if s[i] == 'G' { 1 } else { 0 };
        b[i + 1] = b[i] + if s[i] == 'B' { 1 } else { 0 };
    }

    let mut ans = 0;

    for i in 0..n-2 {
        for j in i+1..n-1 {
            if s[i] == s[j] { continue }
            let d = j - i;
            let c = nokori(s[i], s[j]);
            if j + d <= n - 2 {
                ans += count(j + 1, j + d,  c, &r,&g,&b);
                ans += count(j + d + 1,  n, c,&r,&g,&b);
            } else if j + d == n - 1 {
                ans += count(j + 1, j + d, c,&r,&g,&b);
            } else {
                ans += count(j + 1, n, c,&r,&g,&b);
            }
        }
    }

    put!(ans);
}

use std::io::{self, Write};
use std::str::FromStr;
use std::collections::VecDeque;

struct Scanner { stdin: io::Stdin, buffer: VecDeque<String>, }
impl Scanner {
    fn new() -> Self { Scanner { stdin: io::stdin(), buffer: VecDeque::new() } }
    fn cin<T: FromStr>(&mut self) -> T {
        while self.buffer.len() == 0 {
            let mut line = String::new();
            let _ = self.stdin.read_line(&mut line);
            for w in line.split_whitespace() {
                self.buffer.push_back(String::from(w));
            }
        }
        self.buffer.pop_front().unwrap().parse::<T>().ok().unwrap()
    }
    fn chars(&mut self) -> Vec<char> { self.cin::<String>().chars().collect() }
    fn vec<T: FromStr>(&mut self, n: usize) -> Vec<T> { (0..n).map(|_| self.cin()).collect() }
}


Measured memory_bytes: 2264