using textWatcher for input

Question

I am working an app that display table inputs and a total, i am using a text Watcher to keep truck with changes in the edit text but the issue, when I tried to change inputs the total won't display properly When I erase the input it should be subtracted with the total and when added a new input it should be added with the total.?

var fifthUp = 0  

 floor5_up.addTextChangedListener(object : TextWatcher {
            var a = 0
            override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {
            }
            override fun onTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {
                fifthUp -= a
                Log.i("PO TEXT",p0.toString())
                total5F_up.text = fifthUp.toString()
                a = 0
            }
            override fun afterTextChanged(p0: Editable?) {
                Log.i(TAG, " floor5")
                if(p0.toString() != "") {

                    fifthUp += Integer.parseInt(p0.toString())
                    total5F_up.text = fifthUp.toString()
                    a = Integer.parseInt(p0.toString())
                    findValue( floor5_up, 5,2, 16, 0)
                }
            }
        })