Java 代码

/**4 MDKJ
"Nothing is impossible. Some things are just less likely than others."
    - Jonathan Winters
*/

import java.util.Scanner;

public class Main
{
    public static void main (String[] args)
    {
        Scanner cin = new Scanner(System.in);

        double x1 = cin.nextDouble();
        double y1 = cin.nextDouble();

        double xd = cin.nextDouble() - x1;
        double yd = cin.nextDouble() - y1;

        System.out.println(String.format("%.4f", Math.sqrt(xd * xd + yd * yd)));
    }
}