use proconio::input;

fn main() {
	input! {
		a: usize,
		b: usize,
		c: usize,
		d: usize,
	}

	let mut arr = [a, b, c, d];

	arr.sort();

    let ans = if arr
        .windows(2)
        .all(|arr| arr[1] - arr[0] == 1) {
            "Yes"
        } else {
            "No"
        };

	println!("{ans}");
}