fn getline() -> String{
	let mut __ret=String::new();
	std::io::stdin().read_line(&mut __ret).ok();
	return __ret;
}

fn main(){
	let s=getline();
    let c = 3.0f64;
    let c = c.sqrt();
    let c = c / 36.0f64;
	let x:f64=s.trim().parse().unwrap();
	print!("{} ", c* x * x);
}