use std::io::Read;

fn main() {
	let mut s = String::new();
	std::io::stdin().read_to_string(&mut s).ok();
	let mut v: Vec<f64> = s.split_whitespace().flat_map(str::parse).collect();
	let m = v.pop().unwrap() as usize;
	let u = v[1..].iter().sum::<f64>() / v[0];
	let g = (v[1..].iter().map(|x| (x - u).powi(2)).sum::<f64>() / v[0]).sqrt();
	let a = 50. + if g == 0. { 0. } else { 10. * (v[m] - u) / g };
	println!("{}", if a > 0. { a.floor() } else { a.ceil() })
}