var f,g:text;
    n,j,i,q:longint;
    v:array[1.2000000] of byte;
begin
assign(f,'ciur.in');
assign(g,'ciur.out');
reset(f);
rewrite(g);
read(f,n);
q:=0;
for i:=2 to n do v[i]:=1;
for i:=2 to n do
if v[i]=1 then
   begin
   inc(q);
   j:=2*i;
         while j<=n do
               begin
               v[j]:=0;
               j:=j+i;
               end;
   end;
write(g,q);
close(f);
close(g);
end.