N = int(input())

def check(target):
  buf = str(target)
  mid = len(buf)//2
  head = buf[:mid]
  tail = reversed(buf[mid:])
  zipped = all(list(map(lambda x:x[0]==x[1], zip(head, tail))))
  return zipped
base = 1000000001
mag = 1
checked = 0
while True:
  target = mag*base
  if N < target:
    break
  if check(target) == True:
    checked += 1
  mag+=1
print(checked)