ModuleNotFoundError: No module named 'bs4

I am using streamlit with BeautifulSoup, but when I execute program, it makes error.

There is my code :

import streamlit as st
import pandas as pd
import numpy as np
import requests
from bs4 import BeautifulSoup

r1 = requests.get('https://weather.naver.com/air/02117101')
html = r1.text
soup = BeautifulSoup(html , 'html.parser')
st.write(soup.title.get_text())

There is error massage :
ModuleNotFoundError: No module named 'bs4'

I installed beautifulsoup library but it makes error. I don’t know why it does. How to solve the error?