样例输入
样例输出
样例说明
121212 种方案详情如下:
{1}{2,3},{1}{2,4},{1}{3,4},{2}{1,3},{2}{1,4},{2}{3,4},{3}{1,2},{3}{1,4},{3}{2,4},{4}{1,2},{4}{1,3},{4}{2,3}{1}{2,3},{1}{2,4},{1}{3,4},{2}{1,3},{2}{1,4},{2}{3,4},{3}{1,2},{3}{1,4},{3}{2,4},{4}{1,2},{4}{1,3},{4}{2,3}{1}{2,3},{1}{2,4},{1}{3,4},{2}{1,3},{2}{1,4},{2}{3,4},{3}{1,2},{3}{1,4},{3}{2,4},{4}{1,2},{4}{1,3},{4}{2,3}。