import java.util.Scanner;
public class javaTest {
public static void main(String[] args) {
// TODO Auto-generated method stub
double x1,y1,x2,y2;
Scanner sc=new Scanner(System.in);
while(sc.hasNext()) {
x1=sc.nextDouble();
y1=sc.nextDouble();
x2=sc.nextDouble();
y2=sc.nextDouble();
Point p1=new Point(x1,y1);
Point p2=new Point(x2,y2);
double d=dist(p1, p2);
System.out.printf("The distance is %.2f\n", d);
}
sc.close();
}
static double dist(Point p1,Point p2)
{
double s;
double dx=Math.abs(p2.getX()-p1.getX()) ;
double dy=Math.abs(p2.getY()-p1.getY());
s=Math.sqrt(dx*dx+dy*dy);
return s;
}
}
class Point {
public double x,y;
public Point(double a,double b){
x=a;
y=b;
}
public double getX(){
return x;
}
public void setX(double x){
this.x=x;
}
public double getY(){
return y;
}
public void setY(double y){
this.y=y;
}
}