Program Ciur;
var n,r : longint;
    p : array[2..2000000] of boolean;

procedure Citeste;
var intrare : text;
begin
  assign(intrare,'ciur.in');
  reset(intrare);
  readln(intrare,n);
  close(intrare);
end;

procedure Calculeaza;
var i,j : longint;
begin
  for i:=2 to n do p[i]:=true;
  r:=0;
  p[2]:=true;
  for i:=2 to n do
   if p[i] then begin
     for j:=2 to n div i do p[i*j]:=false;
     r:=r+1;
   end;

end;

procedure Scrie;
var iesire : text;
begin
  assign(iesire,'ciur.out');
  rewrite(iesire);
  write(Iesire,r);
  close(iesire);
end;

begin
  Citeste;
  Calculeaza;
  Scrie;
end.