在具有两列的pandas groupby中选择max of max

import pandas as pd

data = {'Group': ['A', 'A', 'B', 'B', 'C', 'C'],
        'Column1': [10, 20, 30, 40, 50, 60],
        'Column2': [100, 200, 300, 400, 500, 600]}
df = pd.DataFrame(data)

max_values = df.groupby('Group')['Column1', 'Column2'].max()

max_of_max = max_values.max()