What Do You Need to Add to the Class Definition $\quad$

What do you need to add to the class definition to overload operator < so that it applies to the type Money from Display 8.1? Given this extract from the class Money from Display 8.1 of the text.
class Money
{
$\quad$ public:
$\quad$$\quad$ Money( );
$\quad$$\quad$ // other constructors
$\quad$$\quad$ // other public members
$\quad$$\quad$ int getCents( )const;
$\quad$$\quad$ int getDollars( )const;
$\quad$ private:
$\quad$$\quad$ int dollars;
$\quad$$\quad$ int cents;
$\quad$$\quad$ // other private members
};