=1/8*(1/11-1/13-1/13+1/15 +1/13-1/15-1/15+1/17 +...+1/29-1/31-1/31+1/33)
中间的全部抵消掉,只剩下首尾的四项
1/8*（1/11-1/13-1/31+1/33）=10/13299