Maximum talks attended

A conference publishes its single-track schedule as talks[i] = [start, end] in minutes; a talk occupies the half-open span [start, end), so you can walk straight from a talk into one that begins exactly as it ends. You never leave a talk partway through. Return the maximum number of talks you can attend in full. Example: talks [[9,10],[9,11],[10,12]] gives 2.