12 — 12101

for n in range(1000):
  s="9"+"4"*n
  while "94" in s or "644" in s or "444" in s:
    if "94" in s:
      s=s.replace("94","4",1)
    if "644" in s:
      s=s.replace("644","49",1)
    if "444" in s:
      s=s.replace("444","6",1)
  if s.count("4")*18==n:
    print(n)