
ZOJ Problem Set  3012
Once upon a time, there was a temple. And the honor of the monks in the temple is their tower.One day, the Buddhist abbot wants to find out who is the smartest monk in the temple, so he gives the monks a problem: Calculate the area of the tower's shadow at a specific time of the day.
Perhaps the mission is easy to complete with a directly measuring the shadow, but the Buddhist abbot makes it nearly impossible, he said: The tower is formed with N floors, each floor is a hexagon, and every two adjacent floors will be linked by six congruent isosceles trapezoid (For example, floor N links to floor N1, floor 2 links to floor 1, floor 1 links to floor 0). The top of the tower, which can be regarded as floor 0, is a dot (that is, it can be treated as a hexagon with a zero side length). Then floor 1 is the floor under floor 0, floor 2 is under floor 1, floor 3 is under floor 2...floor N is under floor (N  1). Now let R_{i} equals to the side length of hexagon number i, H_{i} equals to the height of floor i (of course it's the height from the bottom), and you know the shadow's length L of a exactly vertically placed stick (Its height exactly equals to 1. We assume that sun light is parallel light, and it is perpendicular to two parallel sides of each hexagon). Input There are several test cases. Output For each test case, you may output a float number S, which represents the area of the tower's shadow. Round S to 4 digits after decimal point. Sample Input
1 1.00
3 0.00 Sample Output
4.2990 Author: FAN, Yuzhe Source: ZOJ Monthly, July 2008 