Problem Statement

Given are integers a, b, c, and d.
We will choose integers x and y such that a ≤ x ≤ b and c ≤ y ≤ d. Find the maximum possible value of x - y here.

Input

Input is given from Standard Input in the following format:
a b
c d

Output

Print the answer.

Constraints

• All values in input are integers.
• -100 ≤ a ≤ b ≤ 100
• -100 ≤ c ≤ d ≤ 100

Sample Input 1

0 10
0 10

Sample Output 1

10

(x, y) = (10, 0) achieves the maximum value x - y = 10.

Sample Input 2

-100 -100
100 100

Sample Output 2

-200

Sample Input 3

-100 100
-100 100

Sample Output 3

200

见题面 Input 部分

见题面 Output 部分