# Problem: Pygmy Hippos

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## Pygmy Hippos

**Input File:** `hippoin.txt`
**Output File:** `hippoout.txt`
**Time Limit:** 1 second

Your backyard has been overrun by adorably tiny hippos, and they are eating the
daisies!

You have a line of N daisies, labelled from 1 to N.
There are three hippos standing next to different daisies ...and they are
already eating them! If you don't act fast, they will eat
all the daisies in your garden.

You have enough plywood to build up to three fences. Each fence will
be built between two daisies that are next to each other. Hippos cannot go
through fences (or over them, or under them, or around them).

Once you have built your fences, the hippos will roam back and forth along the
line of daisies, eating all the daisies they can reach without crossing your
fences. What is the greatest number of daisies you can save?

### Input

Your program should read from the file `hippoin.txt`.

- The first line of input will contain one integer N: the number of daisies.
- The next three lines will each contain an integer describing which daisy
one hippo is currently eating. These will be in increasing order. No two hippos
start at the same daisy.

### Output

Your program should write to the file `hippoout.txt`. Your output file should
contain one line with one integer: the greatest number of daisies you can save.

### Sample Input 1

9
2
5
7

### Sample Input 2

3
1
2
3

### Sample Output 1

4

### Sample Output 2

0

### Explanation

In the first sample case, as illustrated above, if we put a fence between daisies 2 and 3, between
daisies 4 and 5 and between daisies 7 and 8, no hippo will be able to reach
daisies 3, 4, 8 or 9. There is no placement of fences that will save more
daisies, so 4 is the correct answer.

In the second sample case, no matter where you place the three fences you will
not save any daisies, as they are all being eaten.

### Constraints

To evaluate your solution, the judges will run your program against several
different input files. All of these files will adhere to the following bounds: