import java.util.Scanner;

public class Distance
{
   public static void main(String[] args) 
   {
       Scanner input = new Scanner(System.in);
       double x1, y1, x2, y2, distance;
       
       // Read in the coordinates (x1,y1) and (x2,y2)
       System.out.print("x1 = ");
       x1 = input.nextDouble();
       System.out.print("y1 = ");
       y1 = input.nextDouble();
       System.out.print("x2 = ");
       x2 = input.nextDouble();
       System.out.print("y2 = ");
       y2 = input.nextDouble();
       
       distance = Math.sqrt( Math.pow( (x1-x2), 2)
                           + Math.pow( (y1-y2), 2) );
   }
}