public class Solution {
    public int getSum(int a, int b) {
        while(b!=0){
            int c = a & b;
            a = a ^ b;
            b = c << 1;
        }
        return a;
    }
}

public class Queue {
    private Stack<Integer> stack1;
    private Stack<Integer> stack2;

    public Queue() {
        stack1 = new Stack<Integer>();
        stack2 = new Stack<Integer>();
    }
    
    public void push(int element) {
        if (stack2.empty()){
            stack2.push(element);
        } else {
            while (!stack2.empty()){
                stack1.push(stack2.pop());
            }
            stack1.push(element);
            while (!stack1.empty()){
                stack2.push(stack1.pop());
            }
        }
    }

    public int pop() {
        return stack2.pop();
    }

    public int top() {
        return stack2.peek();
    }
}

public class Solution {
    ListNode nthToLast(ListNode head, int n) {
       ListNode first = head;
       ListNode end = head;
       for (int i=0;i<n;i++){
           end = end.next;
       }
       while(end != null){
           end =  end.next;
           first = first.next;
       }
       return first;
    }
}