defmodule Main do
  def input, do: IO.read(:line) |> String.trim
  def ii, do: input() |> String.to_integer
  def li, do: input() |> String.split |> Enum.map(&String.to_integer/1)
  def yn(b), do: IO.puts(if b, do: "Yes", else: "No")

  def primes() do
    Stream.iterate(2, &(&1 + 1))
    |> Stream.unfold(fn s ->
      p = s |> Enum.at(0)
      rest = s |> Stream.filter(fn x -> rem(x, p) != 0 end)
      {p, rest}
    end)
  end

  def main do
    n = ii()

    ps = primes() |> Enum.take_while(fn x -> x <= n end)
    # IO.inspect ps
    IO.puts length(ps)
  end
end