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

class Main {
	public static void main(String[] args) throws Exception {
		new Main().run();
	}

	void run() {
		Scanner sc=new Scanner(System.in);
		int[] a=new int[4];
		for(int i=0;i<a.length;++i)a[i]=sc.nextInt();
		Arrays.sort(a);
		boolean flag=true;
		for(int i=0;i+1<a.length;++i)flag&=a[i]+1==a[i+1];
		System.out.println(flag?"Yes":"No");
	}

	
	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}