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

int n, m;
vector<vector<int>> graph;
vector<int> w;
long long cost;

pair<int, int> dfs(int u, int parent) {
  if (u < m)
    return make_pair(w[u], w[u]);
  vector<int> temp;
  for (int v : graph[u])
    if (v != parent) {
      int a, b;
      tie(a, b) = dfs(v, u);
      temp.push_back(a);
      temp.push_back(b);
      cost -= (b - a);
    }
  sort(temp.begin(), temp.end());
  for (int i = 0; i < temp.size(); ++i)
    cost += abs(temp[temp.size() / 2] - temp[i]);
  return make_pair(temp[temp.size() / 2 - 1], temp[temp.size() / 2]);
}

int main() {
  ios_base::sync_with_stdio(false);
  cin >> n >> m;
  graph.resize(n);
  for (int i = 0; i < n - 1; ++i) {
    int a, b;
    cin >> a >> b;
    --a;
    --b;
    graph[a].push_back(b);
    graph[b].push_back(a);
  }
  w.resize(m);
  for (int i = 0; i < m; ++i)
    cin >> w[i];
  if (n == m) {
    assert(n == 2);
    cout << abs(w[0] - w[1]) << endl;
    return 0;
  }
  cost = 0;
  dfs(m, -1);
  cost /= 2;
  cout << cost << endl;
}