var x,n,k,i:longint;
   a:array[1..20000000] of byte;
   f,g:text;
begin
assign(f,'ciur.in');
assign(g,'ciur.out');
reset(f); rewrite(g);
for i:=1 to n do
a[i]:=1;
a[1]:=0;
for i:=2 to n do
if (a[i]=1) then
 begin
  x:=2*i;
  inc(k);
  while x<=n do
   begin
    a[x]:=0;
    inc(x);
   end;
 end;
writeln(g,k);
close(f);
close(g);
end.