#include <bits/stdc++.h>

#define f first
#define s second
#define pb push_back
#define mp make_pair

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;

const int N = 300500, inf = 1e9, mod = 998244353;
const ll INF = 1e18;

int sum(int a, int b) {
    a += b;
    if (a >= mod)
        a -= mod;
    return a;
}

int sub(int a, int b) {
    a -= b;
    if (a < 0)
        a += mod;
    return a;
}

int mult(int a, int b) {
    return 1ll * a * b % mod;
}

int bp(int a, int b) {
    int res = 1;
    while (b) {
        if (b & 1)
            res = mult(res, a);
        a = mult(a, a);
        b >>= 1;
    }
    return res;
}

int inv(int x) {
    return bp(x, mod - 2);
}

int n, m, a[N];
vector<int> g[N], gq[N];
bool OK;

pii dp[N];

void dfs(int v){
    sort(g[v].begin(), g[v].end());
    int x = -inf;
    dp[v].f = inf;
    dp[v].s = -inf;
    for(auto to : g[v]){
        dfs(to);

        if(dp[to].f == inf)
            continue;

        if(dp[to].f < x)
            OK = 0;
        x = dp[to].s;
        dp[v].f = min(dp[v].f, dp[to].f);
        dp[v].s = max(dp[v].s, dp[to].s);
    }

    for(auto x : gq[v]){
        dp[v].f = min(dp[v].f, x);
        dp[v].s = max(dp[v].s, x);
    }
}
bool check(int k) {
    for(int i = 1; i <= n; i++)
        gq[i].clear();
    for (int i = 0; i < k; i++)
        gq[a[i]].pb(i);
    OK = 1;
    dfs(1);
    return OK;
}

void solve() {
    cin >> n >> m;
    for (int i = 0; i < n - 1; i++) {
        int a, b;
        cin >> a >> b;
        g[a].pb(b);
    }
    for (int i = 0; i < m; i++)
        cin >> a[i];
    int l = 0, r = m;
    while (l <= r) {
        int mid = (l + r) >> 1;
        if (check(mid))
            l = mid + 1;
        else
            r = mid - 1;
    }
    cout << l - 1 << endl;
}

int main() {
#ifdef DEBUG
    freopen("input.txt", "r", stdin);
#endif
    ios_base::sync_with_stdio(false);
    int t = 1;
//    cin >> t;
    for (int i = 1; i <= t; i++) {
//        cout << "Case #" << i << endl;
        solve();
    }
}