class Point{
   int x;
int y;
  Point(int x,int y){
    this.x=x;
    this.y=y;
    }
  static double Distance(Point p1,Point p2){
     double d=Math.sqrt(Math.pow((p2.x-p1.x),2)+Math.pow((p2.y-p1.y),2));
     return d;
   }
 }
import java.lang.*;
import java.util.*;
class Pointdriver{
  public static void main(String args[]){
     Scanner s=new Scanner(System.in);
     int x1=s.nextInt();
     int y1=s.nextInt();
     int x2=s.nextInt();
     int y2=s.nextInt();
     Point p1=new Point(x1,y1);
     Point p2=new Point(x2,y2);
     double res=Point.Distance(p1,p2);
     System.out.println("Distance is"+res);
}
}