def true_code():
    import pandas as pd
    main_data = pd.read_csv("raw_data/main_data.csv")
    main_data["Timestamp"] = pd.to_datetime(main_data["Timestamp"])
    answer = main_data[(main_data["Timestamp"].dt.year == 2023) & (main_data["Timestamp"].dt.month == 12)].groupby("city")["PM2.5"].mean().idxmax()
    print(answer)

true_code()