Time Limit: 2000/1000MS (Java/Others) Memory Limit: 128000/64000KB (Java/Others)

#### Problem Description

We have a special convex that all points have the same distance to origin point.

As you know we can get N segments after linking the origin point and the points on the convex. We can also get N angles between each pair of the neighbor segments.

Now give you the data about the angle, please calculate the area of the convex.

#### Input

There are multiple test cases.

The first line contains two integer *N, D (3 ≤ N ≤ 10, 1 ≤ D ≤ 10)* indicating the number of the points and their distance to origin.

The next lines contains *N* integers indicating the angles. The sum of the *N* numbers is always *360*.

#### Output

For each test case output one float numbers indicating the area of the convex. The printed values should have **3** digits after the decimal point.

#### Sample Input

4 1
90 90 90 90
6 1
60 60 60 60 60 60

#### Sample Output

#### Source

dut200901102

#### Manager