euler268

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace euler268
{
    class Program
    {
        static void Main(string[] args)
        {

            Dictionary<UInt64, List<int>> numbers = new Dictionary<UInt64, List<int>>();
            var primes = PrimesLessThan100();
            
            List<int> ld = new List<int>();
            
            int result = 0;
            for (UInt64 i = (UInt64)Math.Pow(10, 0); i < (UInt64)Math.Pow(10, 4); i++)
            {
                var k=IsDevisableBy4Primes(primes,i);
                if (k!=null)
                {
                    result++;
                    numbers.Add(i,k);
                }
            }
            var test = GetPermutationsMultip(primes,(long) Math.Pow(10, 4));
            double r = 0;// test.Count();
            List<int> multiples = new List<int>();
            //foreach (var item in GetPermutations(primes,4))
            //{
            //    long multipvalue = 1;
            //    foreach (var i in item)
            //    {
            //        multipvalue *= i;
                  
            //    }
            //    if (multipvalue>100000)
            //    {
            //        continue;
            //    }
            //    long g = (long)(Math.Pow(10, 4) / multipvalue)-1;
            //    if (g >= item.Min()) g-= 1;
            //    r += g;
            //}
            foreach (var item in test)
            {
                if (item > Math.Pow(10, 4)) break;
                long g =(long) (Math.Pow(10, 4) / item);
                //if (g >1) g -= 1;
                //for (int i = 2; i < g; i++)
                //{
                //    if (IsPrime(i) && item % i == 0)
                //    {
                //        g -= 1;
                //        break;
                //    }
                //}
                r += g;
                for (int i = 1; i <= g; i++)
                {
                   // if(IsPrime(i)&& item%i==0)
                    multiples.Add(i * item);
                }
            
            }
            //multiples.Sort();
           // multiples.Reverse();
           Console.WriteLine(r+primes.Count());
          
        }
        public static List<int> GetPermutationsMultip(List<int> input,long limit)
        {
            List<int> res = new List<int>();
            foreach (var item in GetPermutations(input, 4))
            {
                int result=1;
                foreach (var i in item)
                {
                    result *= i;
                }
                res.Add(result);
            }
            return res.OrderBy(c=>c).Where(c=>c<limit).ToList();
        }
       static IEnumerable<IEnumerable<T>> GetPermutations<T>(IEnumerable<T> items, int count)
        {
            int i = 0;
            foreach (var item in items)
            {
                if (count == 1)
                    yield return new T[] { item };
                else
                {
                    foreach (var result in GetPermutations(items.Skip(i + 1), count - 1))
                        yield return new T[] { item }.Concat(result);
                }

                ++i;
            }
        }
        public static List<int> IsDevisableBy4Primes(List<int> primes,UInt64 n)
        {
            List<int> divisables = new List<int>();
            int numOfDevisables = 0;
            foreach (var item in primes)
            {
                if (n % (UInt64)item == 0)
                {
                    numOfDevisables++;
                    divisables.Add(item);
                }
                if (numOfDevisables==4)
                {
                    return divisables;
                }
            }
            return null;
        }
        public static List<int> PrimesLessThan100()
        {
            List<int> result = new List<int>();
            for (int i = 2; i < 100; i++)
            {
                if (IsPrime(i))
                {
                    result.Add(i);
                }
            }
            return result;
        }
        public static bool IsPrime(int n)
        {
            int result = 0;
            int start = 2;
            int end = n;
            for (int i = start; i < end; i += 1)
            {
                if (n % i == 0)
                {
                    start = i;
                    end = n / i;
                    result += start == end ? 1 : 2;
                }

            }
            return result == 0;
        }
    }
}