int n = c.Length;
        int minCost = 0;
        int tempCount = 0;
        int previousPurchases = 0;

        Array.Sort(c);

        if(k >= n){
            for(int i = 0; i < n; i++)
                minCost += c[i];
        }
        else{
            for(int i = n - 1; i >= 0; i--){
                if(tempCount == k){
                    tempCount = 0;
                    previousPurchases++;
                }
                minCost += (previousPurchases + 1) * c[i];
                tempCount++;
            }
        }

        return minCost;