import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int[] a = new int[4];
		for (int i = 0; i < a.length; i++) {
			a[i] = sc.nextInt();
		}
		sc.close();

		Arrays.parallelSort(a);
		for (int i = 1; i < a.length; i++) {
			if (a[i - 1] + 1 != a[i]) {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
}