|Codeforces Round #340 (Div. 2)|
Problem C. Watering Flowers
You have to set such $r_1$ and $r_2$ that all the flowers are watered, that is, for each flower, the distance between the flower and the first fountain doesn't exceed $r_1$, or the distance to the second fountain doesn't exceed $r_2$. It's OK if some flowers are watered by both fountains.