import java.util.*;

// Yuki 208
// https://yukicoder.me/problems/no/208

public class Main {
	
	public static void main (String[] args) throws InterruptedException {
		Scanner in = new Scanner(System.in);
		
		long x = in.nextLong();
		long y = in.nextLong();
		long x1 = in.nextLong();
		long y1 = in.nextLong();
		
		long answer = Math.max(Math.abs(x), Math.abs(y));
		if (isBetweenOriginandXY(x, y, x1, y1) && isSameSlope(x, y, x1, y1)) {
			answer++;
		}
		System.out.println(answer);
	}
	
	public static boolean isBetweenOriginandXY(long x, long y, long x1, long y1) {
		if (x < 0 && 0 < y && x1 < 0 && 0 < y1) {
			return x < x1 && y1 < y;
		} else if (x < 0 && y < 0 && x1 < 0 && y1 < 0) {
			return x < x1 && y < y1;
		} else if (0 < x && 0 < y && 0 < x1 && 0 < y1) {
			return x1 < x && y1 < y;
		} else if (0 < x && y < 0 && 0 < x1 && y1 < 0) {
			return x1 < x && y < y1;
		} else {
			return false;
		}
	}
	
	public static boolean isSameSlope(long x, long y, long x1, long y1) {
		return Math.abs(x) * Math.abs(y1) == Math.abs(y) * Math.abs(x1);
	}
}