using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("x1");

        int x1 = Convert.ToInt32(Console.ReadLine());

        Console.WriteLine(" ");

        Console.WriteLine("x2");

        int x2 = Convert.ToInt32(Console.ReadLine());

        Console.WriteLine(" ");

        Console.WriteLine("y1");

        int y1 = Convert.ToInt32(Console.ReadLine());

        Console.WriteLine(" ");

        Console.WriteLine("y2");

        int y2 = Convert.ToInt32(Console.ReadLine());

        Console.WriteLine(" ");

        int x = x2 - x1;

        int y = y2 - y1;

        x = x*x;

        y = y*y;

        int ans = x + y;

        Console.WriteLine(Math.Round(Math.Sqrt(ans),1));

    }

}