package no208;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int x = sc.nextInt();
		int y = sc.nextInt();
		int x2 = sc.nextInt();
		int y2 = sc.nextInt();

		if (!jama(x,y,x2,y2)) {
			System.out.println(Math.max(Math.abs(x), Math.abs(y)));
		}else{
			System.out.println(Math.max(Math.abs(x), Math.abs(y)) + 1);
		}
	}

	public static boolean jama(int x,int y,int x2,int y2) {
		if (Math.abs(x) != Math.abs(y)) {
			return false;
		}
		if (Math.abs(x2) != Math.abs(y2)) {
			return false;
		}
		if (x * x2 < 0 || y * y2 < 0) {
			return false;
		}
		return Math.abs(x2) < Math.abs(x);
	}

}