class MinStack {

 public:

     MinStack(){

         head.next=;

         head.t=;

         m=0x7FFFFFFF;

     }

     void push(int x) {

         node *p=(node *)new(node);

         p->t=x;

         p->next=head.next;

         head.next=p;

         head.t++;

         if(x < m)    //要更新

             m = x;

     }

     void pop() {

         if(==head.t)    return ;

         else if(head.t)

         {

             head.t--;

             if(head.next->t==m) //刚好等于最小值m，要更新最小值

             {

                 int sma=0x7FFFFFFF;

                 node *p=head.next->next;

                 while( p )

                 {

                     if(p->t<sma)

                         sma=p->t;

                     p=p->next;

                 }

                 m=sma;

             }

             head.next=head.next->next;

         }

     }

     int top() {

         if(head.t)

             return head.next->t;

         return ;

     }

     int getMin() {

         return m;

     }

 private:

     struct node

     {

         int t;

         node *next;

     };

     node head;

     int m;

 };