这题问的是区间的方案数，可以看原题面：

The numbers in the set are consecutive if the difference between adjacent elements is exactly 1 when the set is sorted ascendingly. For example, (3, 1, 2) and (5, 1, 2, 4, 3).

Petar wants to know how many different sets of jokes he can see at his party with the listed constraints

简单来说，就是有多少个数字集合 $[L,R]$ 满足可以取到。对于不同的选择节点方案，如果它们选出来的区间 $[L,R]$ 相同，应该算作一个方案。