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#include <iostream>
#include <cstdio>
#include <string>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <cmath>
#include <algorithm>
#include <sstream>
#include <stack>
#include <cstring>
#include <iomanip>
#include <ctime>
#include <cassert>
using namespace std;
#define pb push_back
#define INF 1001001001
#define FOR(i,n) for(int (i)=0;(i)<(n);++(i))
#define FORI(i,n) for(int (i)=1;(i)<=(n);++(i))
#define mp make_pair
#define pii pair<int,int>
#define ll long long
#define vi vector<int>
#define SZ(x) ((int)((x).size()))
#define fi first
#define se second
#define wez(n) int (n); scanf("%d",&(n));
#define wez2(n,m) int (n),(m); scanf("%d %d",&(n),&(m));
#define wez3(n,m,k) int (n),(m),(k); scanf("%d %d %d",&(n),&(m),&(k));
inline void pisz(int n) { printf("%d\n",n); }
template<typename T,typename TT> ostream& operator<<(ostream &s,pair<T,TT> t) {return s<<"("<<t.first<<","<<t.second<<")";}
template<typename T> ostream& operator<<(ostream &s,vector<T> t){FOR(i,SZ(t))s<<t[i]<<" ";return s; }
#define DBG(vari) cout<<"["<<__LINE__<<"] "<<#vari<<" = "<<(vari)<<endl;
#define ALL(t) t.begin(),t.end()
#define FOREACH(i,t) for (__typeof(t.begin()) i=t.begin(); i!=t.end(); i++)
#define TESTS wez(testow)while(testow--)
#define REP(i,a,b) for(int (i)=(a);(i)<=(b);++i)
#define REPD(i,a,b) for(int (i)=(a); (i)>=(b);--i)
#define REMAX(a,b) (a)=max((a),(b));
#define REMIN(a,b) (a)=min((a),(b));
#define IOS ios_base::sync_with_stdio(0););

const int N = 500500;
vi adj[N];
int l[N], r[N];

void dfs (int v, int p) {
   if (adj[v].empty()) return;
   vi events;
   int bal = 0;
   for (int x : adj[v]) if (x != p) {
      dfs(x, v);
      events.pb(l[x]);
      events.pb(r[x]);
      --bal;
   }
   sort(ALL(events));
   for (int ev : events) {
      ++bal;
      if (bal == 0) l[v] = ev;
      else if (bal == 1) r[v] = ev;
   }
}

ll res = 0;
void compute (int v, int p, int pval) {
   int myval;
   if (p == -1) {
      myval = l[v];
   } else {
      if (pval < l[v]) {
         myval = l[v];
      } else if (r[v] < pval) {
         myval = r[v];
      } else {
         myval = pval;
      }
      res += abs(myval - pval);
   }
   for (int x : adj[v]) if (x != p) {
      compute(x, v, myval);
   }
}

int main () {
   wez2(n,m)
   FOR(u,n-1) {
      wez2(a,b)
      adj[a].pb(b);
      adj[b].pb(a);
   }
   FORI(i,m) {
      wez(x)
      l[i] = r[i] = x;
   }
   if (n == m) {
      // n == 2
      pisz(abs(r[1] - r[2]));
      return 0;
   }

   dfs(n, -1);
   compute(n, -1, -1);
   cout << res;
}