import java.util.Stack;

class MyQueue {

    Stack<Integer> s1 = new Stack();

    Stack<Integer> s2 = new Stack();

    // Push element x to the back of queue.

    public void push(int x) {

        s1.push(x);

    }

    // Removes the element from in front of queue.

    public void pop() {

        //思路：s2不空的时候可以直接pop

        if(!s2.empty())

        {

            s2.pop();

        }

        else

        {

            while(!s1.empty())

            {

                s2.push(s1.pop());

            }

            s2.pop();

        }

    }

    // Get the front element.

    public int peek() {

           if(!s2.empty())

        {

            return s2.peek();

        }

        else

        {

            while(!s1.empty())

            {

                s2.push(s1.pop());

            }

            return s2.peek();

        }

    }

    // Return whether the queue is empty.

    public boolean empty() {

        return s1.empty() && s2.empty();

    }

}