import java.util.Stack;

 public class Solution {

     private Stack<Integer> dataStack= new Stack<>();//数据栈

     private Stack<Integer> minStack= new Stack<>();//最小数的栈

     public void push(int node) {

         dataStack.push(node);

         if(minStack.isEmpty() || minStack.peek()>dataStack.peek()){

             minStack.push(dataStack.peek());

         }

         else minStack.push(minStack.peek());

     }

     public void pop() {

         if(!dataStack.isEmpty()) dataStack.pop();

         if(!minStack.isEmpty()) minStack.pop();

     }

     public int top() {

         return dataStack.peek();// 取出数据栈的栈顶元素

     }

     public int min() {

         return minStack.peek();//取出含min函数的栈的栈顶元素

     }

 }