Solve the programming task below in a Python markdown code block.
In Python, a string can be split on a delimiter.  

Example:  

>>> a = "this is a string"
>>> a = a.split(" ") # a is converted to a list of strings. 
>>> print a
['this', 'is', 'a', 'string']

Joining a string is simple:  

>>> a = "-".join(a)
>>> print a
this-is-a-string 

Task 

You are given a string. Split the string on a " " (space) delimiter and join using a - hyphen.   

Function Description   

Complete the split_and_join function in the editor below.   

split_and_join has the following parameters:   

string line: a string of space-separated words   

Returns   

string: the resulting string   

Input Format 

The one line contains a string consisting of space separated words.  

Sample Input 

this is a string   

Sample Output  

this-is-a-string