use std::io::Read;

fn main() {
	let mut s = String::new();
	std::io::stdin().read_to_string(&mut s).ok();
	let n: Vec<u32> = s.split_whitespace().flat_map(str::parse).collect();
	println!(
		"{}",
		if n.windows(2).skip(3).any(|a| { n[0] * a[1] < n[1] * a[0] }) {
			"NO"
		} else {
			"YES"
		}
	);
}