#1950. [Ceoi2006]Link

题目描述

给 N个点N 条边的有向图。 要求添最小的边，使得点1 到达其他所有点的最短路长度不超过K。

输入格式

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.

样例

样例输入

14 4   

1 2   

2 3   

3 4   

4 5   

7 5   

5 6   

6 3   

8 10   

10 9   

9 8   

14 13   

13 12   

12 11   

11 14 

样例输出

3

数据范围与提示

one possible solution is to add the links 1→7, 1→14 and 14→10