#include <cstdio>
#include <cctype>

template <typename T> T read() {
  T res = 0, f = 1;
  char ch = getchar();
  for (; !isdigit(ch); ch = getchar()) if (ch == '-') f = -1;
  for (; isdigit(ch); ch = getchar()) res = (res << 3) + (res << 1) + (ch ^ 48);
  return res * f;
}

#include <algorithm>
typedef long long ll;

const int MAXN = 5e5 + 10;

struct EDGE {
  int u, v, next;
} edge[MAXN << 1];

int head[MAXN], edgeNum;
void AddEdge(int u, int v) {
  edge[++edgeNum] = {u, v, head[u]};
  head[u] = edgeNum;
}

struct Weight {
  int IntervalLeft, IntervalRight;
} weight[MAXN];

ll ans;
int sortArray[MAXN << 1], scnt;
void dfs(int u, int fa) {
  // fprintf(stderr, "%d %d\n", u, fa);
  for (int i = head[u]; i; i = edge[i].next) {
    int v = edge[i].v;
    if (v == fa) continue;
    dfs(v, u);
  }

  scnt = 0;
  for (int i = head[u]; i; i = edge[i].next) {
    int v = edge[i].v;
    if (v == fa) continue;
    sortArray[++scnt] = weight[v].IntervalLeft;
    sortArray[++scnt] = weight[v].IntervalRight;
  }
  if (!scnt) return;

  std::sort(sortArray + 1, sortArray + scnt + 1);
  weight[u].IntervalLeft = sortArray[scnt / 2];
  weight[u].IntervalRight = sortArray[scnt / 2 + 1];

  // fprintf(stderr, "node[%d] updated: left=%d, right=%d\n", u, weight[u].IntervalLeft, weight[u].IntervalRight);

  for (int i = head[u]; i; i = edge[i].next) {
    int v = edge[i].v;
    if (v == fa) continue;
    // fprintf(stderr, "\tweight[%d].left=%d, .right=%d\n", v, weight[v].IntervalLeft, weight[v].IntervalRight);
    if (weight[v].IntervalRight < weight[u].IntervalLeft) {
      ans += weight[u].IntervalLeft - weight[v].IntervalRight;
    } else if (weight[v].IntervalLeft > weight[u].IntervalLeft) {
      ans += weight[v].IntervalLeft - weight[u].IntervalLeft;
    }
  }
}

int n, m;

int main() {
  #ifdef LOCAL
    freopen("!input.in", "r", stdin);
    freopen("!output.out", "w", stdout);
  #elif !defined(ONLINE_JUDGE)
    freopen("starria.in", "r", stdin);
    freopen("starria.out", "w", stdout);
  #endif
  
  n = read<int>(), m = read<int>();
  for (int i = 1; i <= n - 1; ++i) {
    int u = read<int>(), v = read<int>();
    AddEdge(u, v);
    AddEdge(v, u);
  }
  for (int i = 1; i <= m; ++i) {
    weight[i].IntervalLeft = weight[i].IntervalRight = read<int>();
  }
  dfs(n, 0);

  printf("%lld\n", ans);
  return 0;
}