#include <algorithm>
#include <cmath>
#include <cstdio>
#include <iostream>
#include <vector>

using namespace std;

const int N = 500500;

int n;
int m;
vector<int> tree[N];
int l[N];
int r[N];
long long res;

void dfs (int now, int dad) {
	vector<int> t;
	for (auto son : tree[now]) {
		if (son == dad) {
			continue;
		}
		dfs (son, now);
		t.push_back(l[son]);
		t.push_back(r[son]);
	}
	if (now > m) {
		sort (t.begin(), t.end());
		int num = t.size() / 2;
		l[now] = t[num - 1];
		r[now] = t[num];
	}
	for (auto son : tree[now]) {
		if (son == dad) {
			continue;
		}

		if (r[son] < l[now]) {
			res += l[now] - r[son];
		}
		else if (l[now] < l[son]) {
			res += l[son] - l[now];
		}
	}

}

int main () {

	freopen ("starria.in", "r", stdin);
	freopen ("starria.out", "w", stdout);

	cin >> n >> m;
	int u, v;
	for (int i = 1; i < n; i++) {
		cin >> u >> v;
		tree[u].push_back(v);
		tree[v].push_back(u);
	}
	for (int i = 1; i <= m; i++) {
		cin >> l[i];
		r[i] = l[i];
	}

	dfs (n, 0);
	cout << res << endl;
	
	return 0;
}