find the maximum value of a pandas dataframe index
If you know that indices go from 1 to 5844 with none missing, df.shape[0] works.
I have a pandas MultiIndexed pandas dataframe.  I would like to find the maximum value of one of the (numerical, integer) indices.  
That is, the index runs from 1 to 5844.  I want to be able to find the scalar value 5844.  
I realize that I could just set the scalar variable as I know the values which the index takes, but I'd like to be able to find the maximum value in the case when I don't know it.