N = gets.to_i
L = Rational((N - 1).to_s.size, 3).ceil

ans = 0
V = 10 ** L

1.upto(L) do |l|
  (10 ** (l - 1)).upto(10 ** l - 1) do |v|
    x = v * (1 + 10 ** l + 10 ** (2 * l))

    if x <= N
      # pp [v, N, x, l, (1 + 10 ** l + 10 ** (2 * l))]
      ans += 1
    end
  end
end

puts ans