#pragma GCC optimize("Ofast")
#pragma GCC optimize("O3")

#include <bits/stdc++.h>
using namespace std;

#define el '\n'
#define F first
#define S second

typedef long long ll;
typedef long double ld;

bool multipleTestCases = 0, sublime = 0;
const int N = 2e5 + 5, INF = 1e9 + 5, mod = 1e9 + 7, LOG = 22, SQ = 500;

int n, q, qu[N], in[N], out[N], val[N], timer;
vector<int> g[N];
vector<pair<int, int>> ord;
bool fail;
int maxi = 2e5 + 5;
void dfs(int node)
{
    int ls = -1;
  //  cout << g[node].size() << endl;
    for (int i = 0;i < g[node].size();++i)
    {
        int cur = g[node][i];
       // cout << val[cur] << endl;
        if(!val[cur])
            continue;
        if(ls > val[cur])
            maxi = min(maxi, ls - 1);
        ls = val[cur];
    }
    for(auto &i : g[node])
        dfs(i);
}

void doWork()
{
    cin >> n >> q;

    for (int i = 0; i < n - 1; i++)
    {
        int u, v;
        cin >> u >> v;
        g[u].push_back(v);
    }

    for (int i = 1; i <= n; i++)
        sort(g[i].begin(), g[i].end());

    for (int i = 1; i <= q; i++)
    {
        cin >> qu[i];
        if ( !val[qu[i]])
             val[qu[i]] = i;
      //  cout << val[qu[i]] << endl;
    }
    dfs(1);
    cout << min(q,maxi) << el;
}
signed main() {
#ifdef ONLINE_JUDGE
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
#endif
#ifndef ONLINE_JUDGE
    if (sublime) {
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    }
#endif
    int tests = 1;
    if (multipleTestCases) {
        cin >> tests;
    }
    for (int tc = 1; tc <= tests; tc++) {
        doWork();
    }
}