import java.util.*

fun main(args: Array<String>) {
    val scanner = Scanner(System.`in`)
    val x1 = scanner.nextDouble()
    val y1 = scanner.nextDouble()
    val x2 = scanner.nextDouble()
    val y2 = scanner.nextDouble()
    println(Math.sqrt(Math.pow(x1 - x2, 2.toDouble()) + Math.pow(y1 - y2, 2.toDouble())))
}
