Strangely enough, there's been a break-in at the company headquarters!

Unfortunately, the lack of security cameras in the building means that
the criminal(s?) will escape scot-free.

To prevent such a thing from happening again, the company has decided to
purchase some security cameras.

To simplify things a bit, we'll assume the building is very simple - the
various passages in the company can only go north/south or east/west.

Now, these cameras contain mirrors that allow them to have a fairly good
field of view.

Because of distortion and other factors, though, they can only see
"straight" (see diagram).

The company would like to place cameras so that each hallway is
completely covered by one (or more) cameras.

These cameras are expensive, of course, and so you'd like to minimize
the number of cameras required.

#### Input Specification

, the number of hallways.

For each hallway, line:

integers , representing the start and end locations of
the hallway respectively.

Assume the company floor is a 2D plane with being the southwest
corner and the northeast corner.

Each hallway will either have or (not both!).

Parallel hallways will never overlap.

#### Output Specification

The minimum number of cameras required.

#### Sample Input

```
6
1 4 7 4
2 2 2 4
2 2 6 2
6 1 6 6
5 1 6 1
3 6 5 6
```

#### Sample Output

`4`

#### Diagram

By putting cameras in the locations, uh, shown, every building location
is covered.

## Comments