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