Editing 2015 Dec Bronze Problem 1 Fence Painting (section)

== Problem ==

Farmer John is painting his fence. The fence is 1-dimensional, with positions along the fence denoted by integers. Two sections of the fence need to be painted, both described by two integers $a$ and $b$ ($a \le b$), and $c$ and $d$ ($c \le d$), indicating that the interval from $a$ to $b$ and from $c$ to $d$ need to be painted. It's possible that these intervals overlap.

Your task is to compute the total length of the fence that needs to be painted.

The input file, "paint.in", starts with two space-separated integers, $a$ and $b$ ($0 \le a < b \le 100$). The second line of the input contains another two space-separated integers, $c$ and $d$ ($0 \le c < d \le 100$).

The output file, "paint.out", should output one line with one integer – the total length of the fence that needs to be painted.