#include <bits/stdc++.h>

#define LOG(FMT...) fprintf(stderr, FMT)

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;

const int N = 100010;

int n, k;
int a[N], s[N];
ll x[N], y[N];
vector<int> g[N];
vector<pair<pair<ll, int>, int>> greedy[N];

void dfs(int u) {
  s[u] = 1;
  for (int v : g[u])
    if (!s[v]) {
      dfs(v);
      s[u] += s[v];
      greedy[u].emplace_back(make_pair(x[v] - 1, s[v] * 2), v);
    }
  sort(greedy[u].begin(), greedy[u].end(), [&](const pair<pair<ll, int>, int>& lhs, const pair<pair<ll, int>, int>& rhs) { return rhs.first.first - lhs.first.second > lhs.first.first - rhs.first.second; });
  int d = greedy[u].size();
  vector<ll> dp;
  dp.push_back(numeric_limits<ll>::max());
  int pre = 0;
  x[u] = a[u] + min(k - 2 * s[u], 0);
  for (const auto& pr : greedy[u]) {
    x[u] = min(x[u], pr.first.first - pre);
    dp.push_back(min(dp.back(), pr.first.first - pre));
    pre += pr.first.second;
  }
  if (d) {
    vector<ll> suf(d + 1);
    suf[d] = numeric_limits<ll>::max();
    for (int i = d - 1; i >= 0; --i)
      suf[i] = min(suf[i + 1] - greedy[u][i].first.second, greedy[u][i].first.first);
    y[u] = numeric_limits<ll>::min();
    pre = 0;
    for (int i = 0; i < d; ++i) {
      int v = greedy[u][i].second;
      y[u] = max(y[u], min({y[v] - 2 * (s[u] - s[v] - 1) - 1, suf[i + 1] - pre, dp[i], (ll)a[u], a[u] + k - 2LL * (s[u] - s[v])}));
      pre += greedy[u][i].first.second;
    }
  } else
    y[u] = a[u];
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cin >> n >> k;
  for (int rep = 1; rep < n; ++rep) {
    int u, v;
    cin >> u >> v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  for (int i = 1; i <= n; ++i) cin >> a[i];
  dfs(1);
  cout << max(-1LL, y[1]) << '\n';
  return 0;
}