program ciurul;
   var n,i,j,k:longint;
       a:array [1..2000000] of boolean;
       fi,fo:text;
begin
  assign(fi,'ciur.in');
   reset(fi);
  assign(fo,'ciur.out');
   rewrite(fo);
  read(fi,n);
  for i:=2 to n do begin
                if not a[i] then inc(k);
                    j:=i*2;
                     while j<=n do begin
                                  a[j]:=true;
                                      j:=j+i;
                                       end;
                     end;
     write(fo,k);
  close(fo);
end.