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import java.io.IOException;
import java.io.InputStream;
import java.util.Collections;
import java.util.InputMismatchException;
import java.util.LinkedList;

public class roz {
  public static void main(String... args) {
    FastScanner scanner = new FastScanner(System.in);

    int numberOfStations = scanner.nextInt();
    int numberOfForeignStations = scanner.nextInt();

    StationNode[] stationsConnectedTo = new StationNode[numberOfStations + 1];
    for (int i = 0; i < numberOfStations - 1; i++) {
      int stationA = scanner.nextInt();
      int stationB = scanner.nextInt();
      stationsConnectedTo[stationA] = new StationNode(stationB, stationsConnectedTo[stationA]);
      stationsConnectedTo[stationB] = new StationNode(stationA, stationsConnectedTo[stationB]);
    }

    StationNode queueFromRoot;
    {
      queueFromRoot = new StationNode(numberOfForeignStations + 1, null);
      boolean[] isScheduledForVisiting = new boolean[numberOfStations + 1];
      isScheduledForVisiting[queueFromRoot.station] = true;
      StationNode visiting = queueFromRoot;
      while (visiting != null) {
        StationNode connection = stationsConnectedTo[visiting.station];
        while (connection != null) {
          if (!isScheduledForVisiting[connection.station]) {
            isScheduledForVisiting[connection.station] = true;
            visiting.next = new StationNode(connection.station, visiting.next);
          }
          connection = connection.next;
        }
        visiting = visiting.next;
      }
    }

    StationNode queueFromLeafs = null;
    {
      StationNode visiting = queueFromRoot;
      while (visiting != null) {
        queueFromLeafs = new StationNode(visiting.station, queueFromLeafs);
        visiting = visiting.next;
      }
    }

    ArrowNode[] arrows = new ArrowNode[numberOfStations + 1];
    {
      for (int station = 1; station <= numberOfForeignStations; station++) {
        int spacing = scanner.nextInt();
        arrows[station] = new ArrowNode(spacing, true, new ArrowNode(spacing, false, null));
      }
    }

    long totalPrice = 0;
    {
      boolean[] wasVisited = new boolean[numberOfStations + 1];
      StationNode visiting = queueFromLeafs;
      while (visiting != null) {
        wasVisited[visiting.station] = true;

        StationNode connection = stationsConnectedTo[visiting.station];
        while (true) {
          if (connection == null) {
            totalPrice += squash(arrows[visiting.station]);
            break;
          }
          if (!wasVisited[connection.station]) {
            totalPrice += squash(arrows[visiting.station]);
            arrows[visiting.station].next.next = arrows[connection.station];
            arrows[connection.station] = arrows[visiting.station];
            arrows[visiting.station] = null;
            break;
          }
          connection = connection.next;
        }
        visiting = visiting.next;
      }
    }

    System.out.println(totalPrice);
  }

  private static long squash(ArrowNode arrow) {
    long price = 0;

    LinkedList<ArrowNode> arrows = new LinkedList<ArrowNode>();
    ArrowNode adding = arrow;
    while (adding != null) {
      arrows.add(adding);
      adding = adding.next;
    }
    Collections.sort(arrows);

    int left = -1;
    int right = -1;
    while (!arrows.isEmpty()) {
      if (!arrows.getFirst().isRight) {
        left = arrows.getFirst().spacing;
        arrows.removeFirst();
        continue;
      }
      if (arrows.getLast().isRight) {
        right = arrows.getLast().spacing;
        arrows.removeLast();
        continue;
      }
      left = arrows.getFirst().spacing;
      right = arrows.getLast().spacing;
      price += right - left;
      arrows.removeFirst();
      arrows.removeLast();
    }
    arrow.spacing = left;
    arrow.isRight = false;
    arrow.next = new ArrowNode(right, true, null);
    return price;
  }

  private static final class ArrowNode implements Comparable<ArrowNode> {
    int spacing;
    boolean isRight;
    ArrowNode next;

    public ArrowNode(int spacing, boolean isRight, ArrowNode next) {
      this.spacing = spacing;
      this.isRight = isRight;
      this.next = next;
    }

    public int compareTo(ArrowNode o) {
      return spacing - o.spacing;
    }
  }

  private static final class StationNode {
    int station;
    StationNode next;

    public StationNode(int station, StationNode next) {
      this.station = station;
      this.next = next;
    }
  }

  private static class FastScanner {
    private final InputStream stream;
    private final byte[] buf = new byte[1024];
    private int curChar;
    private int numChars;
    private SpaceCharFilter filter;

    public FastScanner(InputStream stream) {
      this.stream = stream;
    }

    public int read() {
      if (numChars == -1) {
        throw new InputMismatchException();
      }
      if (curChar >= numChars) {
        curChar = 0;
        try {
          numChars = stream.read(buf);
        } catch (IOException e) {
          throw new InputMismatchException();
        }
        if (numChars <= 0) {
          return -1;
        }
      }
      return buf[curChar++];
    }

    public int nextInt() {
      int c = read();
      while (isSpaceChar(c)) {
        c = read();
      }
      int sgn = 1;
      if (c == '-') {
        sgn = -1;
        c = read();
      }
      int res = 0;
      do {
        if (c < '0' || c > '9') {
          throw new InputMismatchException();
        }
        res *= 10;
        res += c - '0';
        c = read();
      } while (!isSpaceChar(c));
      return res * sgn;
    }

    public boolean isSpaceChar(int c) {
      if (filter != null) {
        return filter.isSpaceChar(c);
      }
      return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
    }

    public interface SpaceCharFilter {
      public boolean isSpaceChar(int ch);
    }
  }
}