function fak(n: integer): uint64;
var
  i: integer;
  rez: uint64;
begin
  rez := 1;
  for i := 1 to n do
    rez := rez * i;
  fak := rez;
end;

var
  s, i, n: integer;

begin
  readln(n);
  for i := 1 to n do
    s := s + fak(i);
  write(s);
end.