program ciur_erathosthenes;
var n,i,j,t,h:longint;
    d,o:text;
begin
assign(d,'ciur.in');
assign(o,'ciur.out');
reset(d);rewrite(o);
read(d,n);
t:=n-1;
for i:=2 to (n div 2) do
  begin
    j:=i*2;
    while j<=n do
      begin
        t:=t-1;
        for h:=i+1 to (j div 2) do
          if j mod h=0 then begin
                              t:=t+1;
                              break;
                            end;
        j:=j+i;
      end;
  end;
write(o,t);
close(d);close(o);
end.