TypeError: The added layer must be an instance of class Layer. Found: <tensorflow.python.keras.layers.convolutional.Conv2D object at 0x00000000

I got error while learning the Machine Learning and i am not finding help on internet can someone help me correct it:

model= Sequential()

model.add(Conv2D(32,(3,3),input_shape=input_shape))
model.add(Activation('relu'))
model.add(MaxPooling2D(pool_size(2,2)))

model.add(Conv2D(64,(3,3)))
model.add(Activation('relu'))
model.add(MaxPooling2D(pool_size(2,2)))

The error i'm getting is:

<ipython-input-33-e2cf34866813> in <module>
      1 model= Sequential()
      2 
----> 3 model.add(Conv2D(32,(3,3),input_shape=input_shape))
      4 model.add(Activation('relu'))
      5 model.add(MaxPooling2D(pool_size(2,2)))

TypeError: The added layer must be an instance of class Layer. Found: tensorflow.python.keras.layers.convolutional.Conv2D object at 0x000000000504F860>