Suppose we have a series of numbers, num_series. We are interested in the maximum value of the minimum of every overlapping window of size window. 
For example, if num_series is defined as follows, and window = 3 
import pandas as pd num_series = pd.Series([1, 2, 3, 4, 1, 2])
Then the minimum of every window of size three would be [1, 2, 1, 1] and the maximum of those minimums is 2. 
Task: Write a function, max_of_min_windows(num_series, window) which takes in the Series, num_series and window size window and returns the maximum of the minimum values for each window.
df = pd.Series([1, 2, 3, 4, 1, 2]) window = 3
| 0 | |
|---|---|
| 0 | 1 | 
| 1 | 2 | 
| 2 | 3 | 
| 3 | 4 | 
| 4 | 1 | 
| 5 | 2 | 
2.0