private Queue<Integer> q1 = new LinkedList<>();
private Queue<Integer> q2 = new LinkedList<>();
private int top;

// Push element x onto stack.
public void push(int x) {
    q1.add(x);
    top = x;
}

// Removes the element on top of the stack.
public void pop() {
    while (q1.size() > 1) {
        top = q1.remove();
        q2.add(top);
    }
    q1.remove();
    Queue<Integer> temp = q1;
    q1 = q2;
    q2 = temp;
}

// Returns whether the stack is empty.
public boolean empty() {
    return q1.isEmpty();
}

// Get the top element.
public int top() {
    return top;
}