var a:array[1..1000000] of longint;
    i,j,n,k:longint;
begin
  assign(input, 'ciur.in');
  reset(input);
  assign(output, 'ciur.out');
  rewrite(output);
  readln(K);
  n:=1;
  a[1]:=2;  
  i:=3;
  while i<=K do
  begin
    j:=1;
    while (sqr(a[j])<=i) AND not (i mod a[j] = 0) do j:=j+1;
    if i mod a[j]<>0
    then begin
      n:=n+1;
      a[n]:=i;
    end;
    i:=i+2;
  end;
  writeln(N);
end.