input: 
  def create_mnist_classifier():
      """ Create a neural network model in Python using Keras to classify the MNIST data set correctly.
      >>> model = create_mnist_classifier()
      >>> model.input_shape == (None, 784)
      True
      >>> model.output_shape == (None, 10)
      True
      """
  
output:     from keras.models import Sequential
      from keras.layers import Dense
  
      model = Sequential()
      model.add(Dense(128, activation='relu', input_shape=(784,)))
      model.add(Dense(64, activation='relu'))
      model.add(Dense(10, activation='softmax'))
  
      return model