#include <iostream>
#include <string>

using namespace std;

class BuggyStringStackNode {
 public:
  BuggyStringStackNode(const string& str, BuggyStringStackNode* next)
      : val_(str), next_(next) {
  }
  const string& val() { return val_; }
  BuggyStringStackNode* next() { return next_; }
 private:
  const string val_;
  BuggyStringStackNode* next_;
};

class BuggyStringStack {
 public:
  void Push(const string& str) {
    BuggyStringStackNode* new_node = new BuggyStringStackNode(str, head_);
    head_ = new_node;
  }
  const string& Pop() {
    BuggyStringStackNode* popped = head_;
    head_ = head_->next();
    return popped->val();
  }

 private:
  BuggyStringStackNode* head_;
};

// This main() method is only for you to try the code; once you've implemented
// the unit tests, you should either comment it out or change it to invoke the
// tests as described in the documentation.
int main(int argc, char** argv) {
  BuggyStringStack stack;
  stack.Push("Hello\n");
  stack.Push("World\n");
  cout << stack.Pop();
  cout << stack.Pop();
}