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#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <fstream>
#include <sstream>
#include <set>
#include <map>
#include <vector>
#include <list>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <string>
#include <queue>
#include <bitset>		//UWAGA - w czasie kompilacji musi byc znany rozmiar wektora - nie mozna go zmienic
#include <cassert>
#include <iomanip>		//do setprecision
#include <ctime>
#include <complex>
using namespace std;

#define FOR(i,b,e) for(int i=(b);i<(e);++i)
#define FORQ(i,b,e) for(int i=(b);i<=(e);++i)
#define FORD(i,b,e) for(int i=(b)-1;i>=(e);--i)
#define REP(x, n) for(int x = 0; x < (n); ++x)

#define ST first
#define ND second
#define PB push_back
#define MP make_pair
#define LL long long
#define ULL unsigned LL
#define LD long double

const double pi = 3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342;

#define MR 500010

bool done[MR];

vector < int > g[MR];

// na koniec bedziemy jako wartosci brac poczatki wyznaczonych przedzialow
pair < int, int > t[MR];
pair < int, bool > work[MR];

LL res[MR];

void dfs(int nr)
{
	int par = -1;
	done[nr] = 1;
	REP(i, (int)g[nr].size())
		if (!done[g[nr][i]])
		dfs(g[nr][i]);
		else par = g[nr][i];
		// policz przedzialy
		int ilew = 0;
		REP(i, (int)g[nr].size())
			if (g[nr][i] != par)
			{
				work[ilew++] = MP(t[g[nr][i]].ST, 0);
				work[ilew++] = MP(t[g[nr][i]].ND, 1);
			}
		// spr czy lisc
		if (!ilew) return;

		sort(work, work + ilew);
		LL sumPrzed = 0, sumZa = 0, best = 0;
		int ilePrzed = 0, ileZa = 0;
		int p = 0, k = 0;
		// przesun wszystkich na poczatki
		int start = ilew;
		FORD(i, ilew, 1)
		{
			if (work[i].ST == work[0].ST) break;
			if (!work[i].ND)
			{
				sumZa += work[i].ST - work[0].ST;
				ileZa++;
			}
			start = i;
		}
		best = sumPrzed + sumZa;
		int prev = 0;
		for (int i = start; i < ilew;)
		{
			LL d = work[i].ST - work[prev].ST;

			// policz koncowki z poprzedniego przedzialu
			FOR(l, prev, i) ilePrzed += work[l].ND;
			sumPrzed += d*ilePrzed;

			int j = i + 1;
			while (j < ilew && work[j].ST == work[i].ST)j++;

			// policz poczatki z aktualnego
			sumZa -= d*ileZa;
			FOR(l, i, j) ileZa -= !work[l].ND;

			LL sum = sumPrzed + sumZa;
			if (sum == best) k = i;
			else if (sum < best)
			{
				best = sum;
				p = k = i;
			}

			prev = i;
			i = j;
		}

		t[nr] = MP(work[p].ST, work[k].ST);
}

void cnt(int nr)
{
	done[nr] = 0;
	REP(i, (int)g[nr].size())
		if (done[g[nr][i]])
		{
			// uaktualnij dziecko
			//assert(!(t[nr].ST < t[g[nr][i]].ST && t[nr].ND > t[g[nr][i]].ND));
			if (t[g[nr][i]].ND < t[nr].ST) t[g[nr][i]].ST = t[g[nr][i]].ND;
			else if (t[g[nr][i]].ST > t[nr].ND) t[g[nr][i]].ND = t[g[nr][i]].ST;
			else if (t[g[nr][i]].ST <= t[nr].ST) t[g[nr][i]].ST = t[g[nr][i]].ND = t[nr].ST;
			else t[g[nr][i]].ST = t[g[nr][i]].ND = t[nr].ND;
			cnt(g[nr][i]);
			res[nr] += res[g[nr][i]];
			res[nr] += abs(t[nr].ST - t[g[nr][i]].ST);
		}
}

int main()
{
	int n, m;
	scanf("%d%d", &n, &m);
	REP(i, n - 1)
	{
		int a, b;
		scanf("%d%d", &a, &b);a--;b--;
		g[a].PB(b);
		g[b].PB(a);
	}
	REP(i, m)
	{
		int a;
		scanf("%d", &a);
		t[i].ST = t[i].ND = a;
	}
	if (m == n)
	{
		assert(n == 2);
		printf("%d\n", abs(t[0].first - t[1].ST));
		return 0;
	}
	dfs(m);
	cnt(m);
	printf("%lld\n", res[m]);
	return 0;
}