public String addOperator(String s){
        if (position ==0){
            return getMessage();
        }
        if (position ==1){
            if(s.equals("="))
                return getMessage();
            setCalculatorSequence(position,s);
            return getMessage();
        }
        if (position ==2){
            if(s.equals("=")){
                setCalculatorSequence(position,calculatorSequence.get(position -2));
                setCalculatorSequence(position,s);
                setCalculatorSequence(position, runAnOperation(position - 4, position - 2));
                saveMemory();
                return getMessage();
            }
            else {
                setCalculatorSequence(position - 1, s);
                return getMessage();
            }
        }
        if (position ==3)  {
            if(s.equals("=")){
                setCalculatorSequence(position,s);
                setCalculatorSequence(position, runAnOperation(position - 4, position - 2));
                saveMemory();
            }
            else{
                setCalculatorSequence(position,"=");
                setCalculatorSequence(position, runAnOperation(position - 4, position - 2));
                if (!naN){
                    saveMemory();
                    setCalculatorSequence(position, calculatorMemory.get(calculatorMemory.size() - 2));
                    setCalculatorSequence(position,s);
                }
                else
                    saveMemory();
            }
            return getMessage();
        }
        if (position ==4){
            setCalculatorSequence(position,s);
        }

        return getMessage();
    }