qefq

using System;
using System.Linq;

namespace Time_15Min
{
    public 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;
        }

    }

    public class Point
    {
        public int x { get; set; }

        public int y { get; set; }
    }
}