I tried to think of many different approaches to this problem but still can't figure out. Can you guys give me a hint? Thank you so much.

Problem VCIRCLES: http://www.spoj.com/problems/VCIRCLES/

Give N circles. Calculate the total area that these N circles cover. The i-th circle has coordinate of center (Xi, Yi) and radius Ri.

1 ≤ N ≤ 50. -10000 ≤ Yi — Ri, Yi + Ri, Xi — Ri, Xi + Ri ≤ 10000.