The first line of input contains two integers N and K (2 ≤ N ≤ 500 000, 1 ≤ K ≤ 20 000) – the number of pages
and the target maximum number of links to be followed.
Each of the following N lines contains two different integers A and B (1 ≤ A, B ≤ N) meaning that the link on
page A points to page B.
输出格式
The first and only line of output should contain a single integer, the minimum number of additional links
required to make the website K-reachable.
BZPRO