import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Collections;

public class Main {
	public static void main(String[] args) throws Exception {

		BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
		String[] str = reader.readLine().split(" ");
		ArrayList<Integer> n = new ArrayList<>();
		//int min = Integer.MAX_VALUE;
		for (int i = 0; i < 4; i++) {
			n.add(Integer.parseInt(str[i]));
		}
		Collections.sort(n);
		if (n.get(0)+1 == n.get(1) && n.get(1)+1 == n.get(2) && n.get(2)+1 == n.get(3)) {
			System.out.println("Yes");
		}
		else {
			System.out.println("No");
		}
	}
}