import scala.math._

object Main extends App {
  val scanner = new java.util.Scanner(System.in)

  val x1 = scanner.nextDouble
  val y1 = scanner.nextDouble
  val x2 = scanner.nextDouble
  val y2 = scanner.nextDouble

  val output = sqrt(pow(x1 - x2, 2) + pow(y1 - y2, 2))

  println(output)
}