n=int(input())
c=0
for i in range(10000):
  s=str(i)
  if i==0:
    s=""
  for i in range(i==0,10):
    c+=int(s+str(i)+s[::-1])*(10**9+1)<=n
  if s!="":
    c+=int(s+s[::-1])*(10**9+1)<=n
print(c)