package main

import "fmt"

func main() {
	var px, py, qx, qy int
	fmt.Scan(&px, &py, &qx, &qy)

	x_diff := abs(px - qx)
	y_diff := abs(py - qy)

	t2 := x_diff + y_diff

	t := t2/2 + t2%2
	fmt.Println(t)
}

func abs(a int) int {
	if a < 0 {
		return a * -1
	}
	return a
}