text: import os
  import niconico_dl
  from flask import Flask, render_template, redirect, request
  
  app = Flask(__name__)
  
  def check_url(url):
      nico = niconico_dl.NicoNicoVideo(url)
  
      try:
          nico.get_info()
          return True
      except:
          return False
  
  @app.route('/download', methods=['POST'])
  def download():
      url = request.form.get('url')
  
      if check_url(url):
          with niconico_dl.NicoNicoVideo(url) as nico:
              return redirect(nico.get_download_link())
      else:
          return "Error: Invalid URL"
  
  @app.route('/')
  def index():
      return render_template('index.html')
  
  if __name__ == '__main__':
      port = int(os.environ.get('PORT', 5000))
      app.run(host='0.0.0.0', port=port)