int getTotal()
{
    int sum = 0;
    if(goods != "")
    {

        foreach(var l in _rules)
        {
            int letterCount = 0;
            for(int i = 0; i < goods.Lenght; i++)
            {
                if(l.letter == goods[i])
                    letterCount++;
            }
            sum += (letterCount/l.groupNumber)*l.groupPrice + (letterCount % l.groupNumber)*l.price;
        }
    }
    return sum;
}