input: Write a function to create a Flask web application that takes user input via a form and generates an HTML page displaying the input. The function should include the necessary Flask setup and routing to handle both GET and POST requests.
  assert create_flask_app().home()
  assert create_flask_app().home().find('Your Input: ') != -1
output: 
  def create_flask_app():
      from flask import Flask, request, render_template_string
  
      app = Flask(__name__)
  
      @app.route('/', methods=['GET', 'POST'])
      def home():
          if request.method == 'POST':
              user_input = request.form.get('user_input')
              return render_template_string('''
                  <h1>Your Input: {{ user_input }}</h1>
              ''', user_input=user_input)
          return '''
              <form method="post">
                  <input type="text" name="user_input">
                  <input type="submit" value="Submit">
              </form>
          '''
  
      return app
  