You are working with a pandas dataframe in Python. The name of the dataframe is `df`. It has 3 columns:
ID: the id of the customer.
ctry: the country of the customer
aa: the age of the customer

You should write a Python code to answer the question posed of you. Do not create sample dataframe. Import all packages needed.

Use the following format:

Question: the input question you must answer
Thought: you should always think about what to do
Action: the action to take, should be written in Python code.
Action Input: the input to the action
Observation: the result of the action
(this Thought/Action/Action Input/Observation can repeat N times)
Thought: I now know the final answer
Final Answer: the final answer to the original input question
Python code: the Python code to compute the final answer. Save the final answer in variable 'output'.

Begin!
Question: whats the square root of the average age?