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#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>

using namespace std;


struct Vertex {
  int a, b;
  vector<int> n;
  Vertex(): a(-1), b(-1) { }
  ~Vertex() { }
};


typedef vector<Vertex> Graph;


int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  
  int n, m;
  cin >> n >> m;
  
  Graph G(n);
  
  for(int i = 0; i < n - 1; ++i) {
    int u, v;
    cin >> u >> v;
    --u; --v;
    
    G[u].n.push_back(v);
    G[v].n.push_back(u);
  }
  
  for(int u = 0; u < m; ++u) {
    int t;
    cin >> t;
    G[u].a = G[u].b = t;
  }
  
  queue<int> Q;
  for(int i = 0; i < m; ++i) Q.push(i);
  int last = 0;
  
  while(not Q.empty()) {
    int u = Q.front(); Q.pop();
    last = u;
    
    if(G[u].a == -2) {
      vector<int> kek;
      
      for(unsigned int i = 0; i < G[u].n.size(); ++i) {
        int v = G[u].n[i];
        if(G[v].a >= 0) {
          kek.push_back(G[v].a);
          kek.push_back(G[v].b);
        }
      }
      
      nth_element(kek.begin(), kek.begin() + kek.size() / 2 - 1, kek.end());
      G[u].a = kek[kek.size() / 2 - 1];
      nth_element(kek.begin(), kek.begin() + kek.size() / 2, kek.end());
      G[u].b = kek[kek.size() / 2];
    }
    
    for(unsigned int i = 0; i < G[u].n.size(); ++i) {
      int v = G[u].n[i];
      
      if(G[v].a != -1) continue;
      G[v].a = -2;
      Q.push(v);
    }
  }
  
  vector<bool> queued(n, false);
  queue<int> R;
  R.push(last);
  queued[last] = true;
  int t = (G[last].b + G[last].a) / 2;
  G[last].b = G[last].a = t;
  
  int64_t result = 0;
  
  while(not R.empty()) {
    int u = R.front(); R.pop();
    
    for(unsigned int i = 0; i < G[u].n.size(); ++i) {
      int v = G[u].n[i];
      
      if(queued[v]) continue;
      
      int t = G[v].a;
      if(abs(G[v].a - G[u].a) > abs(G[v].b - G[u].a)) t = G[v].b;
      if(G[v].a <= G[u].a and G[u].a <= G[v].b) t = G[u].a;
      G[v].a = G[v].b = t;
      
      result += abs(G[v].a - G[u].a);
      
      R.push(v);
      queued[v] = true;
    }
  }
  
  cout << result << '\n';
  
  return 0;
}