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

public class Main {
    static HashSet<Integer>[] graph;
    static int n;
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] first = br.readLine().split(" ", 2);
        int x1 = Integer.parseInt(first[0]);
        int y1 = Integer.parseInt(first[1]);
        String[] second = br.readLine().split(" ", 2);
        int x2 = Integer.parseInt(second[0]);
        int y2 = Integer.parseInt(second[1]);
        if (Math.abs(x1) == Math.abs(y1) && Math.abs(x2) == Math.abs(y2) && Math.abs(x1) > Math.abs(x2) && (long)x1 * (long)x2 > 0 && (long)y1 * (long)y2 > 0) {
            System.out.println(Math.abs(x1) + 1);
        } else {
            System.out.println(Math.max(Math.abs(x1), Math.abs(y1)));
        }
    }
}