[USER (data scientist)]: What's the most recent date in the dataset? Please generate the code with the output in string type.
My template of code snippet is:

---BEGIN CODE TEMPLATE---

import pandas as pd
import pickle
from decision_company import read_csv_file, convert_to_datetime, get_max, to_list, get_min_value, sort_by_values, get_first_n_rows, create_date_offset, filter_by_date, concatenate_objects, reset_index, rename_columns, bind_dataframe

atp_tennis = read_csv_file('atp_tennis.csv')

# YOUR SOLUTION BEGIN:
<code1>
[GENERATE 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:

# MY SOLUTION BEGIN:
