import java.util.*;
import java.io.*;
import java.math.*;

public class No208 {
	public static int ans = Integer.MAX_VALUE;
	public static int x, y, x2, y2;
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		x = sc.nextInt();
		y = sc.nextInt();
		x2 = sc.nextInt();
		y2 = sc.nextInt();
		sou(0, 0, 0);
		System.out.println(ans);
	}
	public static void sou(int cx, int cy, int cnt) {
		if(cx > x || cy > y) return;
		if(cx == x && cy == y) ans = Math.min(cnt, ans);
		if(cx+1 != x2 || cy+1 != y2) sou(cx+1, cy+1, cnt+1);
		if(cx != x2 || cy+1 != y2) sou(cx, cy+1, cnt+1);
		if(cx+1 != x2 || cy != y2) sou(cx+1, cy, cnt+1);
	}
}