[USER (data scientist)]: What's the most recent date in the dataset? Please generate a value of the most recent date in the ATP tennis dataset.
My template of code snippet is:

---BEGIN CODE TEMPLATE---

import pandas as pd
import pickle
from decision_company import read_csv_file,

# please import the necessary private functions from decision_company first

atp_tennis = read_csv_file('atp_tennis.csv')

# YOUR SOLUTION BEGIN:
<code1>
[COMPLETE YOUR CODE] 
</code1>
# YOUR SOLUTION END

str(last_date)

# save data
pickle.dump(last_date,open("./pred_result/last_date.pkl","wb"))

---END CODE TEMPLATE---

[YOU (AI assistant)]: To find the most recent date, you can use this code:
'''
import pandas as pd
import pickle
from decision_company import read_csv_file,

# please import the necessary private functions from decision_company first

atp_tennis = read_csv_file('atp_tennis.csv')

# YOUR SOLUTION BEGIN:
