#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

const int mn = 2e5+5;
int in[mn], out[mn];
vector<int> adj[mn];

int dfs(int cur, int t = 0) {
	in[cur] = t;
	for (int a : adj[cur]) t = dfs(a, t);
	out[cur] = t;
	return out[cur]+1;
}

int main() {
	int n, m; cin >> n >> m;
	for (int i =0; i < n-1; i++) {
		int a, b; cin >> a >> b;
		adj[a].push_back(b);
	}
	for (int i = 1; i <= n; i++) sort(adj[i].begin(), adj[i].end());
	dfs(1);
	int time = 0;
	int i = 0;
	for (; i < m; i++) {
		int d; cin >> d;
		if (out[d] >= time) {
			time = max(in[d], time);
		}
		else break;
	}
	cout << i << endl;
}