PROGRAMMING:The smile of ly series fell into the well

You all know that! Smile dumped by girlfriend! However, today is the third day of smiling, I didn't go back to my bedroom! Ly can't help but worry, and is ready to go out to the police. Then in the bedroom downstairs, a sewer without a cover found a black smile（ God bless So ly immediately from the side to find a rope ready to pull up smile! It is known that ly can pull a smile up to 3 meters per hour, but every 3 hours, ly has to rest for 1 hour, at this time, the smile will slide down 1 meter. Can you figure out how long it takes ly to pull the smile out of the well!
###Input format:
The depth of the well is a.
###Output format:
Time taken.
###Input example:
Here is a set of inputs. For example:
```in
five
```
###Output example:
The corresponding output is given here. For example:
```out
two
```
`Hint: You can escape when you reach the wellhead.`






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