try
    {
        input = Convert.FromBase64String(CutString(source, num));
    }
    catch
    {
        try
        {
            input = Convert.FromBase64String(CutString(source + "=", num));
        }
        catch
        {
            try
            {
                input = Convert.FromBase64String(CutString(source + "==", num));
            }
            catch
            {
                return null;
            }
        }
    }