tw

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DistanceBetweenPoint
{
    class Program
    {
        static void Main(string[] args)
        {
            var FirstLine = Console.ReadLine().Split().Select(int.Parse).ToArray();

            var firstPoint = new Point()
            {
                x = FirstLine[0],
                y = FirstLine[1]
            };

            var secoundLine = Console.ReadLine().Split().Select(int.Parse).ToArray();

            var secoundPoint = new Point()
            {
                x = secoundLine[0],
                y = secoundLine[1]
            };

            var result = Distance(firstPoint, secoundPoint);
            Console.WriteLine($"{result:f3}");
        }
        public static double Distance(Point firstPoint, Point secoundPoint)
        {
            var squareX = Math.Pow(firstPoint.x  - secoundPoint.x ,2);
            var squareY = Math.Pow(firstPoint.y - secoundPoint.y, 2);

            var result = Math.Sqrt(squareX + squareY);
            return result;
        }
       class Point
       {
        public int x { get; set; }

        public int y { get; set; }
       }
    }
}