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#include <algorithm>
#include <cassert>
#include <cctype>
#include <iostream>
#include <unistd.h>
#include <utility>
#include <vector>
using namespace std;

typedef long long LL;

class Input {
 public:
  Input() { bufpos = bufend = buffer; eof = false; }
  bool Eof() { return eof; }
  char Peek() { if(bufpos == bufend) Grab(); return *bufpos; }
  unsigned char UPeek() { return static_cast<unsigned char>(Peek()); }
  void SkipWS();
  template<class T> T Get();
  void operator()() {}
  template<class Arg, class... Args> void operator()(Arg &arg, Args &... args) {
    arg = Get<Arg>();
    operator()(args...);
  }
 private:
  static const int BUFSIZE = 1<<16;
  char buffer[BUFSIZE];
  char *bufpos;
  char *bufend;
  bool eof;
  void Grab();
};

void Input::Grab() {
  if(eof) return;
  bufpos = buffer;
  bufend = buffer + read(0, buffer, BUFSIZE);
  if(bufend==bufpos) { eof=true; *bufpos=0; }
}

template<> inline char Input::Get<char>() {
  char res = Peek();
  ++bufpos;
  return res;
}

void Input::SkipWS() {
  while(isspace(UPeek())) Get<char>();
}

template<> unsigned Input::Get<unsigned>() {
  SkipWS();
  unsigned x = 0;
  while(isdigit(UPeek())) {
    x = 10u * x + (Get<char>()-'0');
  }
  return x;
}

template<> int Input::Get<int>() {
  SkipWS();
  bool neg = false;
  if(Peek()=='-') { neg=true; Get<char>(); }
  unsigned x = Get<unsigned>();
  if (neg) x = -x;
  return static_cast<int>(x);
}

Input IN;

//----------------

struct Node {
  int degree;
  Node **neighbors;
  Node *parent;
  // Optimal values are in range optMin..optMax, and subtree then costs optCost.
  int optMin;
  int optMax;
  long long optCost;

  Node() : degree{0}, neighbors{nullptr}, parent{nullptr}, optMin{0}, optMax{0},
    optCost{0} {}
};

int numForeign;
vector<Node> nodes; // 16 MB
vector<pair<Node*,Node*>> edges; // 4 MB
vector<Node*> neighborStorage; // 4 MB
Node *root;
vector<Node*> topologicalOrder; // 2 MB

void ReadInput() {
  int n;
  IN(n, numForeign);
  nodes.resize(n);
  edges.resize(n-1);
  for (auto &e : edges) {
    int a, b;
    IN(a, b);
    e.first = &nodes[a-1];
    e.second = &nodes[b-1];
    ++e.first->degree;
    ++e.second->degree;
  }
  for (int i=0; i<numForeign; ++i) {
    Node &node = nodes[i];
    int r; IN(r);
    node.optMin = r;
    node.optMax = r;
  }
}

void ComputeNeighbors() {
  neighborStorage.resize(2 * edges.size());

  // Prepare to fill backwards.
  Node **nextStorage = &neighborStorage[0];;
  for (Node &node : nodes) {
    nextStorage += node.degree;
    node.neighbors = nextStorage;
  }
  assert(nextStorage == &neighborStorage[0] + neighborStorage.size());

  // Fill.
  for (const auto &e : edges) {
    *(--e.first->neighbors) = e.second;
    *(--e.second->neighbors) = e.first;
  }
}

void TopologicalSort() {
  root = &nodes[0];
  topologicalOrder.reserve(nodes.size());

  vector<Node*> st; // 2 MB
  st.reserve(nodes.size());
  st.push_back(root);

  while (!st.empty()) {
    Node *const node = st.back();
    st.pop_back();
    topologicalOrder.push_back(node);
    for (int i=0; i < node->degree; ++i) {
      Node *const x = node->neighbors[i];
      if (x == node->parent) continue;
      x->parent = node;
      st.push_back(x);
    }
  }

  assert(topologicalOrder.size() == nodes.size());
  reverse(topologicalOrder.begin(), topologicalOrder.end());
}

long long Solve() {
  vector<int> kinks;  // 4 MB
  kinks.reserve(2 * nodes.size());

  for (Node *const node : topologicalOrder) {
    if (node >= &nodes[0] + numForeign) {
      // Compute kinks.
      kinks.clear();
      for (int i=0; i < node->degree; ++i) {
        const Node *const child = node->neighbors[i];
        if (child == node->parent) continue;
        kinks.push_back(child->optMin);
        kinks.push_back(child->optMax);
      }
      assert(kinks.size() >= 2u);
      vector<int>::iterator middle = kinks.begin() + kinks.size() / 2;
      nth_element(kinks.begin(), middle, kinks.end());
      node->optMax = *middle;
      node->optMin = *max_element(kinks.begin(), middle);
    }
    node->optCost = 0;
    int val = node->optMin;
    for (int i=0; i < node->degree; ++i) {
      const Node *const child = node->neighbors[i];
      if (child == node->parent) continue;
      node->optCost += child->optCost;
      if (val > child->optMax) {
        node->optCost += (val - child->optMax);
      } else if (val < child->optMin) {
        node->optCost += (child->optMin - val);
      }
    }
  }

  return root->optCost;
}

int main() {
  ReadInput();
  ComputeNeighbors();
  TopologicalSort();
  long long res = Solve();
  cout << res << '\n';
}