Akuya has finally obtained Shinki Hikari's iPhone. Now, he needs to crack the password to gather evidence!

Blindly attempting to crack the password won't work, so Akuya found a note inside Shinki Hikari's phone case. On it was a puzzle! He believes the solution to this puzzle is the phone's password. The puzzle is as follows:

Given a positive integer , the double factorial of is the product of all positive integers with the same odd/even parity as and not exceeding . It is denoted as , for example, .

Find the number of trailing zeros in the decimal representation of the product .

Akuya is just one step away from achieving his revenge. Can you help him?

Input one line containing a positive integer .

Only one line, containing a integer, represents the answer.

11

5

 =