program info;
var n,i,j,c:integer;
    prim:array[1..200005]of boolean;
    f,g:text;
begin
  assign(f,'ciur.in');
  reset(f);
  assign(g,'ciur.out');
  rewrite(g);
  readln(f,n);
    for i:=2 to n do
      prim[i]:=true;
    for i:=2 to n do
      begin
        if prim[i]=true then
          begin
            c:=c+1;

          end;
          j:=i+i;
          prim[j]:=false;
      end;
        writeln(g,c-1);
  close(f);
  close(g);
end.