// Example program
#include <iostream>
#include <string>
#include <vector>
#include <exception>
#include <stdexcept>
template <typename T>
class Stack {
  public:

  T top() {
    if (size() == 0) {
      throw std::runtime_error("Stack is empty");
    }
    return data.back();
  }

  void pop() {
    if (size() != 0) {
        data.erase(data.end() - 1);
    }
  }

  void push(const T& value) {
   data.emplace_back(value);
  }

  std::size_t size() const {
      return data.size();
  }

  void print() {
   print(data.size());
  }

  void print(std::size_t elementCount) {
    for (auto iter = data.crbegin(); iter < data.crbegin() + elementCount; ++iter) {
        std::cout << *iter << std::endl;
    }
  }

  private:
  std::vector<T> data;

};

int main()
{
    Stack<int> stack;
    std::cout << stack.size() << std::endl;
    stack.push(10);
    stack.push(20);
    try {
        std::cout << stack.size() << std::endl;
        stack.print(1);
    } catch (std::exception &e) {
        std::cout << e.what() << std::endl;
    }
}