#![allow(unused_parens)]
#![allow(unused_imports)]
#![allow(non_upper_case_globals)]
#![allow(non_snake_case)]
#![allow(unused_mut)]
#![allow(unused_variables)]
#![allow(dead_code)]

use itertools::Itertools;
use proconio::input;
use proconio::marker::{Bytes, Chars};

#[allow(unused_macros)]
#[cfg(debug_assertions)]
macro_rules! mydbg {
    //($arg:expr) => (dbg!($arg))
    //($arg:expr) => (println!("{:?}",$arg));
      ($($a:expr),*) => {
          eprintln!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
      }
}
#[cfg(not(debug_assertions))]
macro_rules! mydbg {
    ($($arg:expr),*) => {};
}

macro_rules! echo {
    ($($a:expr),*) => {
          $(println!("{}",$a))*
      }
}

use std::cmp::*;
use std::collections::*;
use std::ops::{Add, Div, Mul, Sub};

#[allow(dead_code)]
static INF_I64: i64 = 92233720368547758;
#[allow(dead_code)]
static INF_I32: i32 = 21474836;
#[allow(dead_code)]
static INF_USIZE: usize = 18446744073709551;
#[allow(dead_code)]
static M_O_D: usize = 1000000007;
#[allow(dead_code)]
static PAI: f64 = 3.1415926535897932;

trait IteratorExt: Iterator {
    fn toVec(self) -> Vec<Self::Item>;
}

impl<T: Iterator> IteratorExt for T {
    fn toVec(self) -> Vec<Self::Item> {
        self.collect()
    }
}

trait CharExt {
    fn toNum(&self) -> usize;
    fn toAlphabetIndex(&self) -> usize;
    fn toNumIndex(&self) -> usize;
}
impl CharExt for char {
    fn toNum(&self) -> usize {
        return *self as usize;
    }
    fn toAlphabetIndex(&self) -> usize {
        return self.toNum() - 'a' as usize;
    }
    fn toNumIndex(&self) -> usize {
        return self.toNum() - '0' as usize;
    }
}

trait VectorExt {
    fn joinToString(&self, s: &str) -> String;
}
impl<T: ToString> VectorExt for Vec<T> {
    fn joinToString(&self, s: &str) -> String {
        return self
            .iter()
            .map(|x| x.to_string())
            .collect::<Vec<_>>()
            .join(s);
    }
}

trait StringExt {
    fn get_reverse(&self) -> String;
}
impl StringExt for String {
    fn get_reverse(&self) -> String {
        self.chars().rev().collect::<String>()
    }
}

trait UsizeExt {
    fn pow(&self, n: usize) -> usize;
}
impl UsizeExt for usize {
    fn pow(&self, n: usize) -> usize {
        return ((*self as u64).pow(n as u32)) as usize;
    }
}

use permutohedron::Heap;

fn main() {
    input! {
       N: usize,
       s:Chars,
    }

    let mut ans: usize = 0;

    let mut r = vec![0; N];
    let mut b = vec![0; N];
    let mut g = vec![0; N];
    let mut h = vec![0; 3];
    for i in 0..N {
        if s[i] == 'R' {
            r[i] += 1;
        } else if s[i] == 'G' {
            g[i] += 1;
        } else {
            b[i] += 1;
        }
    }
    let mut r2 = vec![0; N + 1];
    let mut b2 = vec![0; N + 1];
    let mut g2 = vec![0; N + 1];
    for i in 0..N {
        r2[i + 1] = r[i] + r2[i];
        b2[i + 1] = b[i] + b2[i];
        g2[i + 1] = g[i] + g2[i];
    }

    for i in 0..N - 2 {
        if s[i] == 'R' {
            ans += (g2[N] - g2[i + 1]) * (b2[N] - b2[i + 1]);
        } else if s[i] == 'G' {
            ans += (r2[N] - r2[i + 1]) * (b2[N] - b2[i + 1]);
        } else {
            ans += (g2[N] - g2[i + 1]) * (r2[N] - r2[i + 1]);
        }
    }

    // for i in 0..N {
    //     for j in i + 1..N {
    //         let mut f = vec![false; 3];
    //         if s[i] != s[j] {
    //             if s[i] == 'R' {
    //                 f[0] = true;
    //             } else if s[i] == 'G' {
    //                 f[1] = true;
    //             } else {
    //                 f[2] = true;
    //             }
    //             if s[j] == 'R' {
    //                 f[0] = true;
    //             } else if s[j] == 'G' {
    //                 f[1] = true;
    //             } else {
    //                 f[2] = true;
    //             }
    //             if f[0] == false {
    //                 ans += r2[N] - r2[j + 1];
    //             } else if f[1] == false {
    //                 ans += g2[N] - g2[j + 1];
    //             } else {
    //                 ans += b2[N] - b2[j + 1];
    //             }
    //         }
    //     }
    // }

    let mut z = 0;
    mydbg!(ans);

    for step in 1..N {
        for i in 0..N {
            if i + step * 2 >= N {
                continue;
            }
            if s[i] != s[i + step] && s[i + step] != s[i + step * 2] && s[i + step * 2] != s[i] {
                z += 1;
            }
        }
    }

    ans -= z;

    echo!(ans);
}


Measured memory_bytes: 2376