P2944 [USACO09MAR] Earthquake Damage 2 G

Wisconsin has had an earthquake that has struck Farmer John's farm! The earthquake has damaged some of the pastures so that they are unpassable. Remarkably, none of the cowpaths was damaged. As usual, the farm is modeled as a set of $P\ (1 \le P \le 3,000)$ pastures conveniently numbered $1\cdots P$ which are connected by a set of $C\ (1 \le C \le 20,000)$ non-directional cowpaths conveniently numbered $1\dots C$. Cowpath $i$ connects pastures $a_i$ and $b_i\ (1 \le a_i,b_i \le P)$. Cowpaths might connect $a_i$ to itself or perhaps might connect two pastures more than once. The barn is located in pasture $1$. A total of $N\ (1 \le N \le P)$ cows (in different pastures) sequentially contacts Farmer John via moobile phone with an integer message $report_j\ (2 \le report_j \le P)$ that indicates that pasture $report_j$ is undamaged but that the calling cow is unable to return to the barn from pasture $report_j$ because she could not find a path that does not go through damaged pastures. After all the cows report in, determine the minimum number of pastures that are damaged.

Line $1$: Three space-separated integers: $P$, $C$, and $N$. Lines $2\dots C+1$: Line $i+1$ describes cowpath $i$ with two integers: $a_i$ and $b_i$. Lines $C+2\dots C+N+1$: Line $C+1+j$ contains a single integer: $report_j$

Line $1$: One number, the minimum number of damaged pastures.

Only pasture $2$ being damaged gives such a scenario.