package main

import . "fmt"
//import . "math"

func main() {
	var xa,ya,xb,yb int64
	Scan(&xa,&ya,&xb,&yb)
	if ya > yb {
		xa,ya,xb,yb = xb,yb,xa,ya
	}
	p := int64(1)
	for yb < 1e7 {
		p *= 10
		ya *= 10
		yb *= 10
	}
	var mind int64 = 1e18
	var ans float64
	for yp := ya; yp <= yb; yp++ {
		dya := ya - yp
		dyb := yb - yp
		d := xa*xa*p*p+dya*dya+xb+xb*p*p+dyb*dyb
		if d < mind {
			mind,ans = d, float64(yp)/float64(p)
		}
	}
	Println(ans)
}