#include <iostream>
#include <cstdlib>
#include "hydrogen_atom.h"
#include "helium_atom.h"
#include "oxygen_atom.h"
using namespace std;

int main()
{
	const hydrogen_atom h;
	const helium_atom he;
	const oxygen_atom o;

	cout <<  "H belongs to period " << hydrogen_atom::period() << ".\n";
	cout << "He belongs to period " <<   helium_atom::period() << ".\n";
	cout <<  "O belongs to period " <<   oxygen_atom::period() << ".\n";

	return EXIT_SUCCESS;
}