Program Ciurul;
               var i, j, n, nr: 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);
     nr:=0;
             for i:=2 to n do begin
                                   if a[i]=false then begin
                                                           NR:=NR+1;
             for j:=2 to n do begin
                                   if i*j>n then break else a[i*j]:=true;
                              end;
                      end;
              end;
              write(fo,nr);
      close(fo);
end.