max = gets.chomp.to_i
dividor = 10**9+1
cnt=0
idx = 1
num = idx*dividor
while num <= max
  s = num.to_s
  slicer = s.size % 2 ? num/2 : num/2+1
  a = s.slice(0,slicer)
  b = s.reverse.slice(0,slicer)
  cnt+=1 if a==b
  num = (idx+=1)*dividor
end
puts cnt.to_s