var     a:array[1..2000000] of boolean;
        n,nr,i:longint;
        f:text;

procedure prim;
var     i,j:longint;
begin
  for i:=2 to n do
    a[i]:=true;
  for i:=2 to round(sqrt(n)) do
    if a[i] then
      begin
        j:=i;
        while j+i<=n do
          begin
            inc(j,i);
            a[j]:=false;
          end;
      end;
end;

begin
  assign(f,'ciur.in');
  reset(f);
  read(f,n);

  prim;
  nr:=0;
  for i:=2 to n do
    if a[i] then inc(nr);

  assign(f,'ciur.out');
  rewrite(f);
  write(f,nr);
  close(f);
end.