
import java.util.*

fun main(args : Array<String>) {

  val scanner = Scanner(System.`in`)
  val s = scanner.nextLine().split(" ") ;

  val x1 = s[0].toDouble()
  val y1 = s[1].toDouble()
  val x2 = s[2].toDouble()
  val y2 = s[3].toDouble()

  val xLine = x2 - x1
  val yLine = y2 - y1

  val line = Math.sqrt( Math.pow(xLine, 2.0) + Math.pow(yLine, 2.0) )

  println("%.8f".format(line))
}

