using System;

class King
{
	static void Main(String[] args)
	{
		String[] vals;
		int x,y,x2,y2;
		vals = Console.ReadLine().Split(' ');
		x = int.Parse(vals[0]);
		y = int.Parse(vals[1]);
		vals = Console.ReadLine().Split(' ');
		x2 = int.Parse(vals[0]);
		y2 = int.Parse(vals[1]);
		int ax,ay,ax2,ay2;
		ax = Math.Abs(x);
		ay = Math.Abs(y);
		ax2 = Math.Abs(x2);
		ay2 = Math.Abs(y2);

		int steps = Math.Max(ax, ay);
		if(ax == ay && ax2 == ay2 && ax > ax2)
			steps++;
		Console.WriteLine(steps);
	}
}