var
  n, i, j, b: integer;

var
  is_prime: array[2..2000001] of boolean;
var fin,fout:textfile;

begin
assign(fin,'hell.in');
reset(fin);
assign(fout,'hell.out');
rewrite(fout);
  read(fin,n);
  for i := 2 to n do is_prime[i] := true;
  for i := 2 to n do
  begin
    if (is_prime[i])= true then
    begin
      inc(b);
      for j := 2 to trunc(n div i) do is_prime[i * j] := false; 
    end;
  end;
  writeln(fout,b);
  close(fin);
  close(fout);
end.