Program Ciurul;
               var i, j, n, k : longint;
                   u : array[1..2000000] of boolean;
                   fi, fo : text;
begin
      assign(fi,'prob4.in'); reset(fi);
      assign(fo,'prob4.out'); rewrite(fo);
      read(fi,n);
             for i:=2 to n do
                             u[i]:=true;
             k:=0;
             for i:=2 to n do begin
                                   if u[i] then begin
                                                     k:=k+1;
                                                     j:=i;
             while j<=n do begin
                                u[j]:=false;
                                j:=j+i;
                           end;
                    end;
             end;
             write(fo,k);
             close(fo);
end.