import java.util.*;
public class Osho{
	public static void main(String... args){
		Scanner scan = new Scanner(System.in);
		int x=scan.nextInt(),y=scan.nextInt(),x1=scan.nextInt(),y1=scan.nextInt();
		int res = Math.max(x,y);
		if(Math.abs(x) == Math.abs(y) && Math.abs(x1) == Math.abs(y1) && Math.abs(x) > Math.abs(x1)){
			if(x>0 && y>0 && x1>0 && y1>0){
				res++;
			}else if(x>0 && y<0 && x1>0 && y1<0){
				res++;
			}else if(x<0 && y>0 && x1<0 && y1>0){
				res++;
			}else if(x<0 && y<0 && x1<0 && y1<0){
				res++;
			}
		}
		System.out.println(res);
	}
}