public class No_208 {
	static boolean straight(int x, int y) {
		if (x == 0 || y == 0 || Math.abs(x) == Math.abs(y)) {
			return true;
		} else {
			return false;
		}
	}

	static String direction(int x, int y) {
		if (x == 0) {
			if (y > 0)
				return "N";
			else
				return "S";
		} else if (y == 0) {
			if (x > 0)
				return "E";
			else
				return "W";
		} else if (x == y) {
			if (x > 0)
				return "NE";
			else
				return "SW";
		} else {
			if (x > y)
				return "SE";
			else
				return "NW";
		}
	}

	static boolean inTheWay(String dir, int X, int Y, int fuX, int fuY) {
		switch (dir) {
		case "N":
		case "NE":
			if (Y > fuY)
				return true;
			else
				return false;
		case "E":
		case "SE":
			if (X > fuX)
				return true;
			else
				return false;
		case "S":
		case "SW":
			if (Y < fuY)
				return true;
			else
				return false;
		case "W":
		case "NW":
			if (X < fuX)
				return true;
			else
				return false;
		}
		return false;
	}

	public static void main(String[] args) {
		java.util.Scanner sc = new java.util.Scanner(System.in);
		int X, Y, fuX, fuY;
		X = sc.nextInt();
		Y = sc.nextInt();
		fuX = sc.nextInt();
		fuY = sc.nextInt();

		int step = Math.max(X, Y);

		if (straight(X, Y) && straight(fuX, fuY)) {
			String dir = direction(X, Y);
			if (dir.equals(direction(fuX, fuY))) {
				if (inTheWay(dir, X, Y, fuX, fuY)) {
					step += 1;
				}
			}
		}
		System.out.println(step);
		sc.close();

	}

}