var a,b,c,d,i,s:longint;
begin
read(a);
for i:=1 to 1000000 do
if i>a then begin s:=a*i+s;break;end
else begin a:=a-i;s:=i*i+s;end;
write(s);
end.

/**************************************************************
	Problem: 1520
	User: admin
	Language: Pascal
	Result: Wrong Answer
****************************************************************/