import pandas as pd

upper_df = pd.DataFrame()
lower_df = pd.DataFrame()
upper_df["character"] = ["Rachel Green", "Monica Geller", "Phoebe Buffay"]
upper_df["cast"] = ["Jennifer Aniston", "Courteney Cox", "Lisa Kudrow"]
lower_df["character"] = ["Joey Tribbiani", "Chandler Bing", "Ross Geller"]
lower_df["cast"] = ["Matt LeBlanc", "Matthew Perry", "David Schwimmer"]
print("Upper df:")
upper_df
print("Lower df:")
lower_df
print("Concatenated vertically using append method:")
upper_df.append(lower_df)