c# solution:

static int getMinimumCost(int k, int[] c) {

     int howManyFlowers = c.Count();
     Array.Sort(c);
    int cost = 0;
    int multipleCost = 1;
    int couterForMultipleCost = 0;
    if (howManyFlowers <= k)
    {
        //cost = c.Sum();
        return c.Sum();
    }
    else
    {
        do
        {
        couterForMultipleCost++;
        if (couterForMultipleCost > k)
        {
            couterForMultipleCost = 1;
            multipleCost++;
        }
        cost += multipleCost * c[howManyFlowers - 1];
        howManyFlowers -= 1;
        } while (howManyFlowers != 0);
    }
    return cost;
}