program fractii;

var
  n, i,j,  num, z: longint;
  in_f, out_f: text;
  
  t: array[1..100] of boolean;
  ok: boolean;

begin
  assign(in_f, 'fractii.in');
  assign(out_f, 'fractii.out');
  reset(in_f);
  
  readln(in_f, n);
  
  for i := 1 to n do t[i] := true;  {se creeaza un tablou cu elemente de tip boolean}
  for i := 2 to n do
    if t[i] = true then
      begin
      for j := 2 to n div i do
      
        t[i * j] := false;
num+=(i * j) -1;
  
 end;
  rewrite(out_f);
  write(out_f, num);
  close(out_f);
  
end.