import java.util.Scanner;
import java.lang.Math;
public class Main{
public static void main(String[]args){
Scanner in=new Scanner(System.in);
double x1=in.nextDouble();
double y1=in.nextDouble();
double x2=in.nextDouble();
double y2=in.nextDouble();
double d=Math.sqrt((x2-x1)(x2-x1)+(y2-y1)(y2-y1));
System.out.println(String.format(“%.4f”,d));
}
}