import pandas as pd

# create a dataframe
df = pd.DataFrame({'col1': [1, 2, 3, 4, 5],
                   'col2': [10, 9, 8, 7, 6]})

# sort the dataframe by col2 in descending order
sorted_df = df.sort_values(by='col2', ascending=False)

# get the row number of the 3rd largest value in col2
n = 3
row_number = sorted_df.iloc[n-1].name

print(row_number)