#include <vector>
using namespace std;
class MyStack {
   vector <int> x;
public:
   void push(int y) {
      x.push_back(y);
   }
   int top( ) {
     return x.back( );
   }
   void pop( ) {
     x.pop_back( );
   }
   bool empty( ) { return x.begin() == x.end(); }
};