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 sieve(n) do
    t = :ets.new(:prime, [:set, :protected])
    for i <- 2..n do
      case :ets.lookup(t, i) do
        [] ->
          for j <- i+i..n//i do
            :ets.insert(t, {j})
          end
        _ -> nil
      end
    end

    for i <- 2..n, :ets.lookup(t, i) == [], into: [] do
      i
    end
  end

  def main do
    n = ii()
    primes = sieve(n)
    IO.puts length(primes)
  end
end