Problem:
Distance

Write a program which calculates the distance between two points P1(x1, y1) and P2(x2, y2).

Input

Four real numbers x1, y1, x2 and y2 are given in a line.

Output

Print the distance in real number. The output should not contain an absolute error greater than 10-4.

Sample Input

0 0 1 1

Sample Output

1.41421356

Solution in C# (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

namespace CsharpSpiral {
    partial class Program {
        static void Main(string[] args) {
            var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = true };
            Console.SetOut(sw);
            new Program().Solve(new ConsoleInput(Console.In, ' '));
            Console.Out.Flush();
        }
        public void Solve(ConsoleInput cin) {
            var X = cin.ReadDoubleArray(4);
            var dx = X[2] - X[0];
            var dy = X[3] - X[1];
            Console.WriteLine(Math.Sqrt(dx * dx + dy * dy));
        }
        
    }

    static class ExtendClass {
        public static void Swap<T>(this T[] X, int i, int j) {
            T tmp = X[i];
            X[i] = X[j];
            X[j] = tmp;
        }
        public static string Join<T>(this T[] X, string separator = " ") => string.Join(separator, X);
        public static S[] Clone<S>(this S[] src) where S : struct {
            var res = new S[src.Length];
            Array.Copy(src, res, src.Length);
            return res;
        }
    }

    class ConsoleInput {
        private readonly TextReader _stream;
        private readonly char _separator = ' ';
        private readonly Queue<string> inputStream;
        public ConsoleInput(TextReader stream, char separator = ' ') {
            this._separator = separator;
            this._stream = stream;
            inputStream = new Queue<string>();
        }
        public string Read {
            get {
                if(inputStream.Count != 0) return inputStream.Dequeue();
                string[] tmp = _stream.ReadLine().Split(_separator);
                for(int i = 0; i < tmp.Length; ++i)
                    inputStream.Enqueue(tmp[i]);
                return inputStream.Dequeue();
            }
        }
        public string ReadLine { get { return _stream.ReadLine(); } }
        public int ReadInt { get { return int.Parse(Read); } }
        public long ReadLong { get { return long.Parse(Read); } }
        public double ReadDouble { get { return double.Parse(Read); } }
        public string[] ReadStrArray(long N) {
            var ret = new string[N];
            for(long i = 0; i < N; ++i)
                ret[i] = Read;
            return ret;
        }
        public int[] ReadIntArray(long N) { var ret = new int[N]; for(long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
        public long[] ReadLongArray(long N) { var ret = new long[N]; for(long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
        public double[] ReadDoubleArray(long N) { var ret = new double[N]; for(long i = 0; i < N; ++i) ret[i] = ReadDouble; return ret; }
    }
}