def rsum1(lst):
  if not lst: 
    return 0
  else:
    return lst[0] + rsum(lst[1:])

def rsum2(lst):
 def worker(lst,i):
    if i < 0:
      return 0
   return lst[i] + worder(lst,i-1)
 worker(lst,len(lst) - 1)

def rsum3(lst):
  return sum(lst)