var f,g:text;
    n,i,a,b:longint;

function este_prim (x:longint) :boolean;
var i:longint;
begin
  este_prim:=true;
  for i:=2 to trunc(sqrt(x)) do
    if x mod i=0 then begin
      este_prim:=false;
      break;
      end;
end;

begin
  assign(f,'ciur.in');
  assign(g,'ciur.out');
  reset(f);
  rewrite(g);
  readln(f,n);
    for i:=2 to n do
      if este_prim(i)=true
        then inc(a);
  writeln(g,a);
  close(g);
end.