RSOJava#3

import java.util.Scanner;
import java.lang.Math;

public class MyClass {
    public static void main(String args[]) {

        Scanner input = new Scanner(System.in);

        double inputX1 = input.nextDouble();
        double inputY1 = input.nextDouble();
        double inputX2 = input.nextDouble();
        double inputY2 = input.nextDouble();

        double distance = Math.sqrt(Math.pow((inputX2 - inputX1),2)+(Math.pow((inputY2-inputY1),2)));

        System.out.println(distance);

    }
}