public class Solution {

    Stack<Integer> stack1 = new Stack<>();

    Stack<Integer> stack2 = new Stack<>();

    

    public void push(int node) {

        stack1.push(node);

    }

    

    public int pop() {

        if (stack1.empty() && stack2.empty()) {

            throw new RuntimeException("queue is empty");

        }

        if (stack2.empty()) {

            while (!stack1.empty()) {

                stack2.push(stack1.pop());

            }

        }

       return stack2.pop();

    }

}