program cntprim (input , output);
    var N , p , i , s : integer;
        a : array [1..500000] of integer;

  begin
   readln(N);
   s := 0;
   for i := 1 to N do
    a[i] := i;
   p := 2;
   while p * p <= N do
    begin
     for i := 1 to N do
      if i mod p = 0 then
       a[i] := 0;
     i := 1;
     while a[i] = 0 do
      begin
       p := p + 1;
       i := i + 1;
      end
    end;
   for i := 1 to N do
    if a[i] <> 0 then
     s := s + 1;
   writeln(s);
  end.