Select row once and perform calculation swift

I have table view which displays a list of items and every time a row is selected, a checkmark is added and certain amount is added to var total.

If another row is selected it executes same behaviour as above and the previous amount for the deselected row is subtracted. Also the deselected row receives no checkmark.

The problem is that if a row is selected several times, it will keep adding the amount corresponding to the row selected.

What I want is to add the amount corresponding to the row only once regardless of how many times the row is selected.

class EighthViewController: UIViewController, UITableViewDelegate,UITableViewDataSource {

var total = 0

struct Item {
    var name:String // name of the row
    var selected:Bool // whether is selected or not
}

var frequency = [

    Item(name:"Every week",selected: false),
    Item(name:"Every 2 weeks",selected: false),
    Item(name:"Every 4 weeks",selected: false),
    Item(name:"Once",selected: false),
    Item(name:"End of tenancy cleaning", selected: false)
]

@IBOutlet weak var tableView: UITableView!

override func viewDidLoad() {
    super.viewDidLoad()
}


func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return frequency.count
}
func numberOfSectionsInTableView(tableView: UITableView) -> Int {
    return 1
}

// configure the cell
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath)
    -> UITableViewCell     {
    let cell = tableView.dequeueReusableCellWithIdentifier("Cell")
        cell?.textLabel?.text = frequency[indexPath.row].name
    return cell!
}

func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
    tableView.cellForRowAtIndexPath(indexPath)?.accessoryType = .Checkmark

    if indexPath.row == 0 {
    self.total += 30
        print(total)

        } else if indexPath.row == 1 {
        self.total += 30
        print(total)

         } else if indexPath.row == 2 {
           self.total += 30
           print(total)

    } else if indexPath.row == 3 {
        self.total += 40 
          print(total)

    } else if indexPath.row == 4 {
        self.total += 44 
           print(total)
    }
}

func tableView(tableView: UITableView, didDeselectRowAtIndexPath indexPath: NSIndexPath) {
    tableView.cellForRowAtIndexPath(indexPath)?.accessoryType = .None

    if indexPath.row == 0 {
        self.total -= 30
        print(total)

    } else if indexPath.row == 1 {
            self.total -= 30 // delete previous amount
            print(total)


         } else if indexPath.row == 2 {
            self.total -= 30 // delete previous amount
            print(total)


    }  else if indexPath.row == 3 {
        self.total -= 40 // delete previous amount
         print(total)

    } else if indexPath.row == 4 {
        self.total -= 44 // delete previous amount
         print(total)
    }

    }
}