var f,g:text;n,i,k,j,q:longint;
begin
assign(f,'ciur.in');reset(f);
assign(g,'ciur.out');rewrite(g);
readln(f,n);
q:=0;
for i:=2 to n do begin
k:=0;
for j:=2 to i mod 2 do begin
if i mod j=0 then begin inc(k);break;end;
end;
if k=0 then inc(q);
end;
write(g,q);
end.