One_Task_Is_Not_Enough

using System;
using System.Text;
using System.Collections.Generic;

class Program
{
    static int GetLastLampIndex(bool[] lamps)
    {
        int length = lamps.Length;
        int count = length;

        for (int i = 0; i < length; i++)
        {
            int step = i + 2;
            for (int j = i; j < length; j += step)
            {
                if (lamps[j] == false)
                {
                    lamps[j] = true;
                    count--;
                    if (count == 0)
                    {
                        return (j + 1);
                    }
                }
            }
        }
        return 0;

    }

    static void Main()
    {
        int N = int.Parse(Console.ReadLine());

        bool[] lamps = new bool[N];

        int lastLampIndex = GetLastLampIndex(lamps);
        Console.WriteLine(lastLampIndex);

    }

}