How many darts do you need to throw?

You are given a dartboard of radius $$r$$ and an infinite number of darts. When you throw a dart at the dartboard, it always strikes the dartboard, but you don't necessarily control where it strikes.

You are about to throw $$n$$ darts. What is the minimum value of $$n$$ such that there must be a pair of darts that are closer than $$r$$ to each other?

 Note: The point of each dart is one-dimensional. Darts can be thrown onto the edge of the dartboard.

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