Two Spheres, One Hundred Balconies

A glassmaker testing a new formula has exactly two identical glass spheres and access to a tower with $100$ numbered balconies. There is an unknown critical balcony $N$: a sphere dropped from balcony $N$ or higher shatters, while a drop from any lower balcony leaves it unharmed and reusable. A shattered sphere is gone for good. What is the minimum number of drops that guarantees identifying $N$ exactly, whatever it turns out to be, and what is the strategy?