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#include <bits/stdc++.h>

using namespace std;

const int MAXN = 5e5+10;

typedef long long int ll;
typedef pair<int, ll> pill;

const ll INF = 1000000000000000000LL;

#define mp make_pair
#define pb push_back
#define st first
#define nd second

int n, m, p[MAXN];
vector<int> g[MAXN];
vector<pill> r[MAXN];

void dfs_up(int u) {
	if (u <= m) return;
	//r[u].clear();
	set<int> candidates;
	for (int i = 0; i < int(g[u].size()); i++) {
		int v = g[u][i];
		if (v == p[u]) continue;
		p[v] = u;
		dfs_up(v);
		for (int j = 0; j < int(r[v].size()); j++) candidates.insert(r[v][j].st);
	}
	
	r[u].clear();
	
	while (!candidates.empty()) {
		r[u].pb(mp(*candidates.begin(), 0));
		candidates.erase(candidates.begin());
	}
	/*if (int(candidates.size())%2 == 0) {
		r[u].pb(mp(candidates[int(candidates.size())/2-1], 0));
		r[u].pb(mp(candidates[int(candidates.size())/2], 0));
	}
	else {
		int i = int(candidates.size())/2;
		if (i-1 >= 0) r[u].pb(mp(candidates[i-1], 0));
		r[u].pb(mp(candidates[i], 0));
		if (i+1 < int(candidates.size())) r[u].pb(mp(candidates[i+1], 0));
	}*/
}

void dfs_down(int u) {
	
	set<int> candidates;
	for (int i = 0; i < int(g[u].size()); i++) {
		int v = g[u][i];
		for (int j = 0; j < int(r[v].size()); j++) {
			candidates.insert(r[v][j].st);
		}
	}
	
	r[u].clear();
	
	while (!candidates.empty()) {
		r[u].pb(mp(*candidates.begin(), 0));
		candidates.erase(candidates.begin());
	}
	
	/*if (int(candidates.size())%2 == 0) {
		r[u].pb(mp(candidates[int(candidates.size())/2-1], 0));
		r[u].pb(mp(candidates[int(candidates.size())/2], 0));
	}
	else {
		int i = int(candidates.size())/2;
		if (i-1 >= 0) r[u].pb(mp(candidates[i-1], 0));
		r[u].pb(mp(candidates[i], 0));
		if (i+1 < int(candidates.size())) r[u].pb(mp(candidates[i+1], 0));
	}*/
	
	for (int i = 0; i < int(g[u].size()); i++) {
		int v = g[u][i];
		if (v == p[u] || v <= m) continue;
		dfs_down(v);
	}
}

void dfs_solve(int u) {
	
	for (int i = 0; i < int(g[u].size()); i++) {
		int v = g[u][i];
		if (v == p[u]) continue;
		dfs_solve(v);
	}
	
	for (int c = 0; c < int(r[u].size()); c++) {
		r[u][c].nd = 0;
		for (int i = 0; i < int(g[u].size()); i++) {
			int v = g[u][i];
			if (v == p[u]) continue;
			ll tmp = INF;
			for (int k = 0; k < int(r[v].size()); k++) {
				tmp = min(tmp, abs(r[u][c].st-r[v][k].st) + r[v][k].nd);
			}
			r[u][c].nd += tmp;
		}
		//printf("r[%d][%d] = (%d, %lld)\n", u, c, r[u][c].st, r[u][c].nd);
	}
}

int main() {
	scanf("%d%d", &n, &m);
	for (int i = 1; i < n; i++) {
		int u, v; scanf("%d%d", &u, &v);
		g[u].pb(v); g[v].pb(u);
	}
	for (int i = 1; i <= m; i++) {
		int _r; scanf("%d", &_r);
		r[i].pb(mp(_r, 0));
	}
	
	ll kochamjulie = INF;
	
	dfs_up(n);
	dfs_down(n);
	dfs_up(n);
	dfs_down(n);
	dfs_solve(n);
	
	for (int i = 0; i < int(r[n].size()); i++) {
		kochamjulie = min(kochamjulie, r[n][i].nd);
	}
	
	printf("%lld\n", kochamjulie);
	
	return 0;
}