def consecutive(arr):
    return (max(arr) - min(arr) - len(arr) + 1) if len(arr) > 0 else 0

'''
Create the function consecutive(arr) that takes an array of integers and return
 the minimum number of integers needed to make the contents of arr consecutive
 from the lowest number to the highest number.

For example:
 If arr contains [4, 8, 6] then the output should be 2 because two numbers need 
 to be added to the array (5 and 7) to make it a consecutive array of numbers
 from 4 to 8. Numbers in arr will be unique.
'''
