PROGRAMMING:Product of even numbers

Find the product of all even numbers from 1 to n$$ n\le 20$$)
###Input format:
Enter the integer n.
###Output format:
Even product from 1 to n
###Input example:
Here is a set of inputs. For example:
```in
five
```
###Output example:
The corresponding output is given here. For example:
```out
eight
```







answer：If there is no answer, please comment