var fi,fo:text;
    n,i,j:int64;
    prim:array[1..2000010]of byte;
    ct:longint;
begin
  assign(fi,'ciur.in'); reset(fi);
  assign(fo,'ciur.out'); rewrite(fo);
  read(fi,n);
  i:=3;
  ct:=1;
  while i<=n do
    begin
      if prim[i]=0 then
        begin
          j:=i*i;
          inc(ct);
          while j<=n do
            begin
              prim[j]:=1;
              inc(j,i);
            end;
        end;
      inc(i,2);
    end;
  writeln(fo,ct);
  close(fi);
  close(fo);
end.