program ciur;

var f : textfile;
    n,i,j, k:longint;
    ePrim:array[2..2000000] of boolean;

begin
    assign(f, 'ciur.in');
    reset(f);
    read(f, n);
    close(f);

   k := 0;
   for i := 2 to n do ePrim[i] := true;
   for i := 2 to n do
   begin
     if (ePrim[i]) then
       begin
       inc(k);
       for j := 2 to trunc(n div i) do ePrim[i*j] := false;
     end;
   end;

    assign(f, 'ciur.out');
    rewrite(f);
    write(f, k);
    close(f);
end.