编程题：length of semicircular arc

Input the radius of the circle and calculate the length of semicircular arc
(using the pi constant in math module)
Formula for the length of a circle：C=2π r





### Input Specification:

Input the radius, which can be a floating point number

### Output Specification:

the length of semicircular arc, and keep 2 decimal places for the result.




### Sample Input:

Write a sample input here. For example:

in
2


### Sample Output:

Write the corresponding sample output here. For example:

out
L=6.28









答案：若无答案欢迎评论