import scala.io.StdIn._
import scala.math._

object Main {
  def distance(s: String): Double = {
    val Array(x1, y1, x2, y2) = s.split(" ").map(_.toInt)
    sqrt(pow(abs(x1 - x2), 2) + pow(abs(y1 - y2), 2))
  }

  def main(args: Array[String]): Unit = {
    val point = readLine()
    println(distance(point))
  }
}