PROGRAMMING:Find the circumference of a circle
Input the radius r of the circle, find its perimeter and output.
###Input format:
Enter a real number greater than zero without any additional characters.
###Output format:
Output according to the format of "s = perimeter", perimeter is a real number with 6 decimal places, without any additional characters.
###Input example:
```in
one
```
###Output example:
```out
s=6.280000
```
answer：If there is no answer, please comment
###Input format:
Enter a real number greater than zero without any additional characters.
###Output format:
Output according to the format of "s = perimeter", perimeter is a real number with 6 decimal places, without any additional characters.
###Input example:
```in
one
```
###Output example:
```out
s=6.280000
```
answer：If there is no answer, please comment