import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            double x1 = sc.nextDouble();
            double y1 = sc.nextDouble();
            double x2 = sc.nextDouble();
            double y2 = sc.nextDouble();
            double temp =Math.sqrt(((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)*1.0));
            System.out.println(String.format("%.2f", temp));
            }
    }
}