package main

import "fmt"

func main() {
	var x, y, x1, y1 int
	fmt.Scan(&x, &y, &x1, &y1)
	var ans int
	if absInt64(x) == absInt64(y) && absInt64(x1) == absInt64(y1) && x > x1 {
		ans += 1
	}
	ans += max(absInt64(x), absInt64(y))
	fmt.Println(ans)
}

func max(a, b int) int {
	if a > b {
		return a
	} else {
		return b
	}
}

func absInt64(x int) int {
	if x < 0 {
		x *= -1
	}
	return x
}