[USER (data scientist)]: Cool! Now, I'd like to know how many matches each player played. Can you help me with that? Please generate the code with the output in series type.
My template of code snippet is:

---BEGIN CODE TEMPLATE---

import pandas as pd
import numpy as np
import pickle
from decision_company import read_csv_file, check_elements_in_list, assert_series, logical_and, logical_or, count_unique_values, fill_missing_values, create_dataframe, reset_index

atp_tennis = read_csv_file('atp_tennis.csv')

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

print(matches_played)

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

---END CODE TEMPLATE---

[YOU (AI assistant)]: Sure thing! We can count the occurrences of each player in the 'Player_1' and 'Player_2' columns and add them up. Here's how:

# MY SOLUTION BEGIN:
