import java.util.*;
import java.util.Collections;
import java.util.stream.Collectors;

public class Main {

  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    ArrayList<Integer> list = new ArrayList<Integer>();
    for (int i = 0; i < 4; i++) {
      list.add(sc.nextInt());
    }
    Collections.sort(list);
    if (list.get(0) + 1 == list.get(1) && list.get(1) + 1 == list.get(2) && list.get(2) + 1 == list.get(3)) {
      System.out.println("Yes");
    } else {
      System.out.println("No");
    }
  }
}