using System;

public class Program {
    public static void Main() {
        int[] target = Array.ConvertAll(Console.ReadLine().Split(), value => int.Parse(value));
        int[] obstacle = Array.ConvertAll(Console.ReadLine().Split(), value => int.Parse(value));
        bool flag = false;
        if (Math.Abs(target[0]) == Math.Abs(target[1]) && Math.Abs(obstacle[0]) == Math.Abs(obstacle[1]) && Math.Abs(target[0]) > Math.Abs(obstacle[0])) {
            if (target[0] * obstacle[0] > 0 && target[1] * obstacle[1] > 0) {
                flag = true;
            }
        }
        Console.WriteLine(Math.Max(Math.Abs(target[0]), Math.Abs(target[1])) + (flag ? 1 : 0));
    }
}