var i,j,n,cnt:integer;
    v:array[1..20000] of integer;
    f,g:text;
begin
cnt:=0;
assign(f,'ciur.in');reset(f);
assign(g,'ciur.out');rewrite(g);
read(f,n);
for i:=2 to trunc(sqrt(n)) do
        if v[i]=0 then begin
                       for j:=2 to (n div i) do
                       v[i*j]:=1;
                       end;
for i:=2 to n do
if v[i]=0 then inc(cnt);
write(g,cnt);
close(f);
close(g);
end.