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: Accepted)

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace Main
{
    public static class Program
    {
        static void Main(string[] arg)
        {
            double r = int.Parse(Console.ReadLine());
            //var array = GetIntList(Console.ReadLine());
            double answer = 0;

            answer = Math.Pow(r,2) * 3;

            Console.WriteLine(answer);
            Console.ReadLine();
 
        }
        
        #region libraries
        private static int[] GetIntList(string line)
        {
            return line.Split(' ').Select(x => int.Parse(x)).ToArray();
 
        }
        private static double[] GetDoubleList(string line)
        {
            return line.Split(' ').Select(x => double.Parse(x)).ToArray();
 
        }
        private static ulong[] GetUlongList(string line)
        {
            return line.Split(' ').Select(x => ulong.Parse(x)).ToArray();
        }
        private static long[] GetLongList(string line)
        {
            return line.Split(' ').Select(x => long.Parse(x)).ToArray();
        }
        private static int SearchNearest(this IEnumerable<int> list, int target)
        {
            var min = list.Min(c => Math.Abs(c - target));
            return list.First(c => Math.Abs(c - target) == min);
        }
        public static bool IsOdd(int i)
        {
            return i % 2 == 1 ? true : false;
        }
        public static int Gcd(int a,int b)
        {
            if(a < b)
            {
                Gcd(b, a);
            }
            while (b != 0)
            {
                var rm = a % b;
                a = b;
                b = rm;
            }
            return a;
        }
        #endregion
    }
}