package main

import (
	"fmt"
	"math"
)

func main() {
	var x, y, x1, y1 float64
	fmt.Scan(&x, &y, &x1, &y1)
	var ans float64
	if (x == 0 && x1 == 0 && y > y1) || (y == 0 && y1 == 0 && x > x1) {
		ans += 2
	}
	ans += max(math.Abs(x1-x), math.Abs(y1-y))
	fmt.Println(ans)
}

func max(a, b float64) float64 {
	if a > b {
		return a
	} else {
		return b
	}
}