#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N = 5e5 + 10;
vector<int> G[N];
int w[N];
int L[N], R[N];
int n, m, res;

void dfs(int x, int xfa)
{
  vector<int> S;
  if (x <= m)return;
  for (auto y : G[x]) if (y != xfa)
  {
      dfs(y, x);
      S.push_back(L[y]), S.push_back(R[y]);
    }
  sort(S.begin(), S.end());
  int sz = S.size();
  if (sz & 1)  L[x] = R[x] = S[sz / 2];
  else         L[x] = S[sz / 2 - 1], R[x] = S[sz / 2];
  for (auto y : G[x]) if (y != xfa)
    {
      if (L[x] > R[y])  res += L[x] - R[y];
      else if (L[x] < L[y])  res += L[y] - L[x];
      else  res += 0;
    }
}

signed main()
{
  ios::sync_with_stdio(False), cin.tie(0), cout.tie(0);
  cin >> n >> m;
  for (int i = 1, a, b; i < n; i++)
  {
    cin >> a >> b;
    G[a].push_back(b);
    G[b].push_back(a);
  }
  for (int i = 1; i <= m; i++)
    cin >> w[i], L[i] = R[i] = w[i];

  if (n == 2)
  {
    cout << abs(w[1] - w[2]) << "\n";
    return 0;
  }

  dfs(m + 1, 0);

  cout << res << "\n";

  return 0;
}