|Codeforces Round #195 (Div. 2)|
One beautiful day Vasily the bear painted 2m circles of the same radius R on a coordinate plane. Circles with numbers from 1 to m had centers at points (2R - R, 0), (4R - R, 0), ..., (2Rm - R, 0), respectively. Circles with numbers from m + 1 to 2m had centers at points (2R - R, 2R), (4R - R, 2R), ..., (2Rm - R, 2R), respectively.
Naturally, the bear painted the circles for a simple experiment with a fly. The experiment continued for m2 days. Each day of the experiment got its own unique number from 0 to m2 - 1, inclusive.
On the day number i the following things happened:
Help Vasily, count the average distance the fly went along the coordinate plane during each of these m2 days.
The first line contains two integers m, R (1 ≤ m ≤ 105, 1 ≤ R ≤ 10).
In a single line print a single real number — the answer to the problem. The answer will be considered correct if its absolute or relative error doesn't exceed 10 - 6.
Figure to the second sample