Adv2016/D19.1/Program.cs

using System;
using System.Collections;

namespace D19._1
{
    class Program
    {
        static void Main(string[] args)
        {
            var ba = new BitArray(int.Parse(args[0]), true);
            int n = ba.Length;

            int i = 0;
            while (n > 1)
            {
                i++;
                if (i >= ba.Length) i -= ba.Length;
                while (!ba[i])
                {
                    i++;
                    if (i >= ba.Length) i -= ba.Length;
                }
                ba.Set(i, false);
                n--;
                while (!ba[i])
                {
                    i++;
                    if (i >= ba.Length) i -= ba.Length;
                }
            }

            for (var j = 0; j < ba.Length; j++)
            {
                if (ba.Get(j))
                {
                    Console.WriteLine($"The answer is : {j+1}");
                    break;
                }
            }
        }
    }
}