import pandas as pd

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

# get the row number of the 3rd largest value in col2
n = 3
row_number = df['col2'].argsort()[::-1][n-1]

print(row_number)