
fun main(args: Array<String>) {
    val (x1, y1, x2, y2) = readLine()!!.split(" ").map { it.toDouble() }
    val d = Math.sqrt( (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2) )
    println("%5f".format(d))
}
