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

using namespace std;

int n;
int m;
long long ret = 0;
vector<bool> visited;
vector<int> boundary;
vector<int> r;
vector<pair<int, int> > edges;

pair<int, int> Dfs(const int a) {
  pair<int, int> p;
  if (a < m) {
    p = make_pair(r[a], r[a]);
  } else {
    visited[a] = true;
    vector<int> mis;
    vector<int> mas;
    for (int i = boundary[a]; i < boundary[a + 1]; ++i) {
      if (!visited[edges[i].second]) {
        p = Dfs(edges[i].second);
        mis.push_back(p.first);
        mas.push_back(p.second);
      }
    }
    sort(mis.rbegin(), mis.rend());
    sort(mas.begin(), mas.end());
    int i = 0;
    while (mis[i] > mas[i]) {
      ret += mis[i] - mas[i];
      ++i;
    }
    if (i == 0) 
      p = make_pair(mis[i], mas[i]);
    else if (2 * i < mis.size())
      p = make_pair(max(mas[i - 1], mis[i]), min(mis[i - 1], mas[i]));
    else
      p = make_pair(mas[i - 1], mis[i - 1]);
  }
  // cerr << a << ' ' << p.first << ' ' << p.second << endl;
  return p;
}

void Go() {
  visited.resize(0);
  visited.resize(n, false);
  Dfs(n - 1);
}

int main() {
  scanf("%d%d", &n, &m);
  vector<int> u(n - 1), v(n - 1);
  for (int i = 0; i < n - 1; ++i) {
    scanf("%d%d", &u[i], &v[i]);
    --u[i];
    --v[i];
  }
  r.resize(m);
  for (int i = 0; i < m; ++i) scanf("%d", &r[i]);
  if (n == m) {
    for (int i = 0; i < n - 1; ++i) ret += abs(r[u[i]] - r[v[i]]);
  } else {
    for (int i = 0; i < n - 1; ++i) {
      edges.push_back(make_pair(u[i], v[i]));
      edges.push_back(make_pair(v[i], u[i]));
    }
    sort(edges.begin(), edges.end());
    int i = 0;
    while (i < edges.size()) {
      while (edges[i].first >= boundary.size()) boundary.push_back(i);
      ++i;
    }
    while (boundary.size() <= n) boundary.push_back(i);
    Go();
  }
  printf("%lld\n", ret);
  return 0;
}