import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int aX = scanner.nextInt();
int aY = scanner.nextInt();
int bX = scanner.nextInt();
int bY = scanner.nextInt();
double n=Math.sqrt((aX-bX)*(aX-bX)+(aY-bY)*(aY-bY));
System.out.println(String.format("%.3f", n));
}
}