# import necessary libraries
import pandas as pd

# define your series
s = pd.Series([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])

# use apply() function with a lambda function
new_series = s.apply(lambda x: x if x % 3 == 0 else float('NaN'))

# drop NaN values and get the index
positions = new_series.dropna().index

# convert into series and print
result = pd.Series(positions)
print(f"Positions of Multiples of 3: \n{result}")