ex=[0,3,6]

def iter(start):
  spoke=dict()
  lastSpokeD=dict()
  turn=0
  nextSpeak=None
  for i in start:
    turn+=1
    spoke[i]=turn
    yield i
    nextSpeak=0
    
  while True:
    turn+=1
    yield nextSpeak
    lastSpoke=spoke.get(nextSpeak)
    spoke[nextSpeak]=turn

    if lastSpoke is None:
      nextSpeak=0
    else:
      nextSpeak=turn-lastSpoke
    
    if turn%3000000==0:
      print(f"turn {turn} of 30000000 ({100*turn/30000000.0}%)")

import itertools
print(list(itertools.islice(iter(ex), 10)))

def nth(start, n):
  return next(x for i,x in enumerate(start) if i==n-1)

# print(nth(iter([0,3,6]), 30000000))
print(nth(iter([5,1,9,18,13,8,0]), 30000000))