program domino;

uses crt;

var
	n, i, j, br, m:longint;

begin
	clrscr;
  readln(n);
  for i:=0 to n do
  	begin
    	if i=0 then
      	m:=0
      else
    		Inc(m);
  		for j:=m to n do
    		br:=br+(i+j);
    end;
  writeln(br);
  readln;
end.