cannot implicitly convert type string to int

Question

 public int GetChannel(string mac)
        {            
            while ((netshline = sr.ReadLine()) != null)
            {
                if(netshline.IndexOf("Channel") > 0)
                {
                   mac = netshline.Substring(netshline.IndexOf(":") + 1).ToString();            
                    
                }               
            }
            return mac;
        }

in return mac i am getting error