def eras(n):
  siv=range(n+1)
  siv[1]=0
  sqn=int(round(n**0.5))
  for i in range(2,sqn+1):
    if siv[i]!=0:
        siv[2*i:n/i*i+1:i]=[0]*(n/i-1)
  return filter(None,siv)