fn main() {
	let mut s = String::new();
	std::io::stdin().read_line(&mut s).ok();
	let mut v: Vec<i64> = s.split_whitespace().flat_map(str::parse).collect();
	if v[1] < 100 * v[0] {
		println!("can't exchange");
		return;
	}
	let d = [10000, 5000, 2000, 1000, 500, 100];
	let c: Vec<_> = d.iter().map(|d| (v[1] / d, v[1] %= d).0).collect();
	if c[5] >= v[0] {
		println!("no exchange");
		return;
	}
	println!("{}", (v[0] - c[5] + 4) / 5 * 5 + c[5]);
}