5.1

program prog;
var
   a, b, s, i, j : longint;
begin
  Readln(a);
  b := 0;
  for i := 1 to a do begin
    s := 1;
    for j := 2 to i do
      s := s * j;
    b := b + s;
  end;
  writeln(b);
end.