Python only saves last picture taken

I am new to programming with Python and the Raspberry Pi, and for my first project i wanted to play the official "Push button stop motion" code from the official raspberry pi camera guide (https://projects.raspberrypi.org/en/projects/push-button-stop-motion)

I wired up the button sucessfully and didn’t change one thing in the code + downloaded and installed the picamera. The button works fine and takes pictures, but it only saves the last taken picture on the desktop. I tried adding an ongoing "i" but it doesn’t seem to work, can anybody help?

from datetime import datetime
from gpiozero import Button 
import picamera 
import time

b=Button(2) 
pc=picamera.PiCamera() 
running = True 
timestamp=datetime.now() 
def picture():         
    pc.capture('pic'+str(timestamp)+'.jpg') 
    
pc.start_preview() 
b.when_pressed=picture 
try: 
    while running:  
        print('Active')
        time.sleep(1) 
    
except KeyboardInterrupt: 
    pc.stop_preview() 
    running = False