program pascal;
var f,g:text; i,n,d,nr:longint;  s:array[1..2000000] of byte;
   procedure ciur;
   begin
   for i:=2 to trunc(sqrt(n)) do
   if s[i]=0 then
    for d:=2 to (n div i) do s[i*d]:=1;
   end;

begin
assign(f,'ciur.in'); reset(f);
assign(g,'ciur.out'); rewrite(g);
read(f,n);
ciur;
nr:=0;
for i:=2 to n do
if s[i]=0 then inc(nr);
write(g,nr);
close(f);
close(g);
end.