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

fn main(){
	let s=getline();
	let a:Vec<_>=s.trim().split(' ').collect();
	let n: f64 = a[0].parse().unwrap();
	let mut now = 1.0;
	
	

	print!("{} ", (1..100000).fold(0.0, |src, val| {
	  now *= n;
	  return src + now * (1.0-n) * val as f64;
	}));
}