class Solution

 {

 public:

     void push(int node) {

         stack1.push(node);

     }

     int pop() {

         if (stack2.empty()) {

             while (!stack1.empty()) {

                 stack2.push(stack1.top());

                 stack1.pop();

             }

         }

         int ret = stack2.top();

         stack2.pop();

         return ret;

     }

 private:

     stack<int> stack1;

     stack<int> stack2;

 };