Flowers problem

Problem:
You and your K-1 friends want to buy N flowers. Flower number i has host ci. Unfortunately the seller does not like a customer to buy a lot of flowers, so he tries to change the price of flowers for customer who had bought flowers before. More precisely if a customer has already bought x flowers, he should pay (x+1)*ci dollars to buy flower number i.
You and your K-1 firends want to buy all N flowers in such a way that you spend the as few money as possible.
Input:
The first line of input contains two integers N and K.
next line contains N positive integers c1,c2,…,cN respectively.
Output:
Print the minimum amount of money you (and your friends) have to pay in order to buy all n flowers.
Sample onput :
3 3
2 5 6
Sample output :
13
Explanation :
In the example each of you and your friends should buy one flower. in this case you have to pay 13 dollars.
Constraint : 1 less than or equal to N,K less than or equal to 100 and each ci is not more than 100,000



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

namespace FlowersDemo
{
    class Solution
    {
        static void Main(String[] args)
        {
            int N, K;
            string NK = Console.ReadLine();
            string[] NandK = NK.Split(new Char[] { ' ', '\t', '\n' });
            N = Convert.ToInt32(NandK[0]);
            K = Convert.ToInt32(NandK[1]);

            int[] C = new int[N];

            string numbers = Console.ReadLine();
            string[] split = numbers.Split(new Char[] { ' ', '\t', '\n' });
           
            double result = 0;
            int i = 0;
            foreach (string s in split)
            {
                if (s.Trim() != "")
                {
                    C[i++] = Convert.ToInt32(s);
                    if (N == K)
                        result += Convert.ToInt32(s);
                }
            }
            if (N != K)
            {
                Array.Sort(C);
                int counter = 0;
                for (int a = N - 1; a >= 0; a--)
                {
                    result += Math.Ceiling((double)(counter/K)+1) * C[a];
                    counter++;
                }

            }

            Console.WriteLine((int)result);
        }
    }
}