program ciur;
type vector=array[2..2000000] of boolean;
var a:vector;
    i,o:text;
    n,c,f,g:longint;
begin
  c:=0;
  assign(i,'ciur.in');
  reset(i);
  readln(i,n);
  close(i);
  for f:=2 to n do
    a[f]:=true;
  for f:=2 to n do
    if a[f] then
      begin
        c:=c+1;
        g:=f+f;
        while g<=n do
          begin
            a[g]:=false;
            g:=g+f
          end
      end;
  assign(o,'ciur.out');
  rewrite(o);
  write(o,c);
  close(o)
end.