var
f,g:text;
i,j,n,k:longint;
ok:boolean;


solutie: array[1..200000] of integer;
begin
assign(f,'ciur.in');
reset(f);
assign(g,'ciur.out');
rewrite(g);


 k:=1;
 solutie[1]:=2;
read(f,n);

for i:=3 to n do begin
ok :=true;

for j:=1 to k do
if i mod solutie[j]=0 then begin ok:=false;
                                break;end;


if ok=true then begin
k:=k+1;
solutie[k]:=i;end;
end;



write(g,k);
close(f);
close(g);
end.