Help with a synchronous counter

Attached is a partial schematic of a homework problem that I need help with. The situation is as follows: A pill manufacturer needs to fill each bottle with 100 pills. As each pill is dropped into the bottle, a detector generates a clock pulse.
a. I need this to operate as a synchronous counter
b. Using the NAND gate I need to complete the circuit such that the counter resets to zero AFTER the 100th pill has dropped.
Any help on this is much appreciated.

I recommend for You a down-counter with BCD pgm-inputs.Symply set it to 100, count down, and give an output on zero.