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#include <algorithm>
#include <cstdlib>
#include <iostream>
#include <utility>
#include <vector>
using namespace std;

namespace {
  class Solver {
    private:
      int n;
      int m;

      using Range = pair<int, int>;

      vector<vector<int>> neigh;
      vector<int> width;

      void dfs(int v, vector<int>& res, vector<int>& parent) const
      {
        if (v < m) return;
        for (auto const& w: neigh[v]) {
          if (w == parent[v]) continue;
          parent[w] = v;
          dfs(w, res, parent);
        }
        res.push_back(v);
      }

      static int cost(Range const& r, int x)
      {
        if (x < r.first) return r.first - x;
        if (x > r.second) return x - r.second;
        return 0;
      }

      void calculate(int v, vector<Range>& range, vector<long long>& res, vector<int> const& parent) const
      {
        res[v] = 0;
        vector<int> subs;
        subs.reserve(2 * neigh[v].size());
        for (auto const& w: neigh[v]) {
          if (w == parent[v]) continue;
          subs.push_back(range[w].first);
          subs.push_back(range[w].second);
          res[v] += res[w];
        }
        auto mid = subs.size() / 2 - 1;
        nth_element(subs.begin(), subs.begin() + mid, subs.end());
        range[v].first = subs[mid];
        range[v].second = *min_element(subs.begin() + mid + 1, subs.end());

        auto x = range[v].first;
        for (auto const& w: neigh[v])
        {
          if (w == parent[v]) continue;
          res[v] += cost(range[w], x);
        }
      }

    public:
      Solver(int n_, int m_): n{n_}, m{m_}, neigh(n), width(m)
      {
      }

      void add(int a, int b)
      {
        neigh[a].push_back(b);
        neigh[b].push_back(a);
      }

      void set(int a, int r)
      {
        width[a] = r;
      }

      long long operator()() const
      {
        if (n == 2) {
          return abs(width[0] - width[1]);
        }

        vector<int> todo;
        todo.reserve(n - m);
        vector<int> parent(n);
        parent[m] = -1;
        dfs(m, todo, parent);

        vector<Range> range(n);
        for (int i = 0; i < m; ++i) {
          range[i] = {width[i], width[i]};
        }

        vector<long long> res(n);

        for (auto const& v: todo) {
          calculate(v, range, res, parent);
        }

        return res[m];
      }
  };
}

int main()
{
  iostream::sync_with_stdio(false);
  cin.tie(nullptr);

  int n, m;
  cin >> n >> m;

  Solver solver{n, m};

  for (int i = 1; i < n; ++i) {
    int a, b;
    cin >> a >> b;
    solver.add(a-1, b-1);
  }

  for (int i = 0; i < m; ++i) {
    int r;
    cin >> r;
    solver.set(i, r);
  }

  cout << solver() << '\n';

  return 0;
}