Problem:
Score : 100 points

Problem Statement

It is known that the area of a regular dodecagon inscribed in a circle of radius a is 3a^2.

Given an integer r, find the area of a regular dodecagon inscribed in a circle of radius r.

Constraints

1 \leq r \leq 100

r is an integer.

Input

Input is given from Standard Input in the following format:

r

Output

Print an integer representing the area of the regular dodecagon.

Sample Input 1

4

Sample Output 1

48

The area of the regular dodecagon is 3 \times 4^2 = 48.

Sample Input 2

15

Sample Output 2

675

Sample Input 3

80

Sample Output 3

19200

Solution in C# (Mono 4.6.2.0) (judge verdict: Runtime Error)

using System;
using System.Collections.Generic;
using System.Linq;
 
public class Solution
{
    public static void Main()
    {
      string str = Console.ReadLine();
      string[] arr = str.Split(' ');
      var N = double.Parse(arr[0]);
      var D = double.Parse(arr[1]);
      // 1人が確認できる木の本数は、(i+D) - (i-D) + 1 = 2D+1のため、
      // 求まる人数をa人とすると、a(2D+1)>=Nとなる
      // 2D+1>0のため、a>=N/(2D+1)を満たす最小の整数をもとめればよい
      double cal = N / (2 * D + 1);
      var result = Math.Ceiling(cal);

      Console.WriteLine($"{result}");
    }
}