public static Stack<Integer> one(Queue<Integer> q1, Queue<Integer> q2)
    {
        Stack<Integer> s1 = new Stack<Integer>();
        Stack<Integer> s2 = new Stack<Integer>();
        Stack<Integer> res = new Stack<Integer>();

        int temp=0, sum;
        while(!q1.isEmpty())
        s1.push(q1.remove());
        while(!q2.isEmpty())
        s2.push(q2.remove());

        while(!s1.isEmpty() && !s2.isEmpty()) // <---THE QUESTION
        {
            sum = s1.pop()+s2.pop()+temp;
            if(sum<10)
            {
                res.push(sum);
                temp = 0;
            }
            else
            {
                res.push(sum%10);
                temp=sum/10;
            }
        }

        while(!s1.isEmpty())
        {
            sum=s1.pop()+temp;
            res.push(sum);
            temp=0;
        }

        while(!s2.isEmpty())
        {
            sum=s2.pop()+temp;
            res.push(sum);
            temp=0;
        }

        return res;

    }