Here is an interesting article:
Your Health and How Calcium Can Help
And here about the amounts:
What is the recommended amount of calcium to consume each day and how much calcium is too much per day? - Milk ProCon.org
I am not a fan of such supplements... Anyway, you can calculate how much calcium you take per day (don't forget that even many vegetables contain calcium) and how much you would need to be right. Your doctor's question doesn't sound too smart, if he gave you advice at least he should have given you complete advice. There is obviously a difference between taking a supplement of 100mg and taking 500mg a day.
Here you have an interesting table with foods and meals that contain calcium:
National Bone Health Campaign: Parents: List of Foods with Calcium | DNPA | CDC
(it's not on the list, but olives have a lot of calcium too!)