use std::io::Read;

fn main() {
	let mut s = String::new();
	std::io::stdin().read_to_string(&mut s).ok();
	let n: Vec<f64> =
		s.split_whitespace().skip(1).flat_map(str::parse).collect();
	println!(
		"{}",
		1000.0 - 1000. * n.iter().fold(1., |t, a| t * (1000. - a) / 1000.)
	)
}