<code csharp>
using System;

namespace teststruct
{	
    class Program
    {
        struct Point {
            public double x;
            public double y;
        }

        static void ReadPoint(ref Point p)
        {
            p.x = double.Parse(Console.ReadLine());
            p.y = double.Parse(Console.ReadLine());			
        }

        static double Distance(Point p1, Point p2)
        {
            return Math.Sqrt(
                (p1.x-p2.x)*(p1.x-p2.x) + 
                (p1.y-p2.y)*(p1.y-p2.y));
        }

        public static void Main(string[] args)
        {
            Point p1 = new Point();
            ReadPoint(ref p1);
            Point p2 = new Point();
            ReadPoint(ref p2);
            Console.WriteLine("{0}",Distance(p1,p2));
            Console.ReadKey(true);
        }
    }
}
</code>