Problem:
Score : 100 points

Problem Statement

Print the circumference of a circle of radius R.

Constraints

1 \leq R \leq 100

All values in input are integers.

Input

Input is given from Standard Input in the following format:

R

Output

Print the circumference of the circle.
Your output is considered correct if and only if its absolute or relative error from our answer is at most 10^{-2}.

Sample Input 1

1

Sample Output 1

6.28318530717958623200

Since we accept an absolute or relative error of at most 10^{-2}, 6.28 is also an acceptable output, but 6 is not.

Sample Input 2

73

Sample Output 2

458.67252742410977361942

Solution in C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using static System.Console;
using static MyUtil;
using System.Collections.Generic;
using System.Linq;
using System.Text;

class Program
{
    static void Main()
    {
        int input = int.Parse(ReadLine());
        WriteLine(input * 2 * Math.PI);

#if DEBUG
        ReadKey();
#endif
    }
}

static class MyUtil
{
    /// <summary>
    /// 指定の桁のビットを取得します。
    /// </summary>
    /// <param name="num"></param>
    /// <param name="count">取得する桁。</param>
    /// <returns></returns>
    public static int GetBit(this int num, int count)
    {
        int mask = (int)Math.Pow(2, count - 1);
        return (num & mask) == 0 ? 0 : 1;
    }

    /// <summary>
    /// <c>int</c>を2進数ビット配列に変換します。
    /// </summary>
    /// <param name="num"></param>
    /// <returns></returns>
    public static int[] ToBitArray(this int num)
    {
        const int size = sizeof(int) * 8;
        var array = new int[size];
        for (int i = 0; i < size; i++)
        {
            array[i] = num.GetBit(size - i);
        }
        return array;
    }

    public static long[] ReadlongArray()
    {
        return ReadLine().Split(' ').Select(s => long.Parse(s)).ToArray();
    }

    public static int[] ReadintArray()
    {
        return ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();
    }

    /// <summary>
    /// <see cref="IEnumerable{T}"/>の各要素を並べてコンソールに出力します。各要素の間には半角スペースが一つ入ります。
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="ts"></param>
    public static void WriteToConsole<T>(this IEnumerable<T> ts)
    {
        StringBuilder stringBuilder = new StringBuilder();
        foreach (T t in ts)
        {
            stringBuilder.Append(t.ToString());
            stringBuilder.Append(" ");
        }
        stringBuilder.Remove(stringBuilder.Length - 1, 1);
        Console.WriteLine(stringBuilder.ToString());
    }
}