import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int[] arr = new int[4];
        for (int i = 0; i < 4; i++) {
            arr[i] = sc.nextInt();
        }
        Arrays.sort(arr);
        if (arr[0] + 1 == arr[1] && arr[1] + 1 == arr[2] && arr[2] + 1 == arr[3]) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        }
    }
}