I am trying to do image classification using VGG16 pre-trained model. For the same, I did the following:

```
vgg16_model = keras.applications.vgg16.VGG16()

```

The type of the model is as follows:

```
type(vgg16_model)

```

And the result is:

```
tensorflow.python.keras.engine.training.Model

```

Then, I defined a Sequential model as:

```
model = Sequential()

```

Then, I tried to convert the `vgg16_model` into sequential by:

```
for layer in vgg16_model.layers:
    model.add(layer)

```

It shows me an error as follows:

```
TypeError: The added layer must be an instance of class Layer. Found: < tensorflow.python.keras.engine.input_layer.InputLayer object at 0x1ddbce5e80>**

```

It would be great if anyone could help me on this one.