input: Write a python function to extract the price of a product from a given URL using BeautifulSoup.
  assert extract_price('https://example.com/product') == 'Price of the product is: $10'
  assert extract_price('https://example.com/product2') == 'Price of the product is: $20'
  assert extract_price('https://example.com/product3') == 'Price of the product is: $15'
output: def extract_price(url):
      import requests
      from bs4 import BeautifulSoup
      
      response = requests.get(url)
      soup = BeautifulSoup(response.content, 'html.parser')
      price = soup.find('span', class_='product-price').text.strip()
      return f'Price of the product is: {price}'