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 steps = Math.Max(Math.Abs(x), Math.Abs(y));
		if(Math.Abs(x) == Math.Abs(y) && Math.Abs(x2) == Math.Abs(y2))
			steps++;
		Console.WriteLine(steps);
	}
}