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#define NDEBUG

#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <set>
#include <cassert>

using namespace std;
using ll = long long;
using range = pair<int, int>;

#define MAXX 500001
int n, m;
vector<int> E[MAXX];
int UnsolvedAdj[MAXX];
range SolutionRanges[MAXX];
struct CmpStations
{
	bool operator () (int s1, int s2);
};
set<int, CmpStations> Q;
int Values[MAXX];
vector<int> NoValueStations;
int Out[MAXX];

void Read();
void PrepareQ();
void ProcessQ();
void SpecifyValues();
void CalcAndPrintResult();

int main()
{
	Read();
	PrepareQ();
	ProcessQ();
	SpecifyValues();
	CalcAndPrintResult();
	return 0;
}

void Read()
{
	scanf("%d%d", &n, &m);
	for(int i = 1; i < n; ++i)
	{
		int v, u;
		scanf("%d%d", &v, &u);
		E[v].push_back(u);
		E[u].push_back(v);
		if(v > m) ++UnsolvedAdj[u];
		if(u > m) ++UnsolvedAdj[v];
	}
	for(int i = 1; i <= m; ++i)
	{
		int r;
		scanf("%d", &r);
		SolutionRanges[i] = {r, r};
		Values[i] = r;
	}
}

void PrepareQ()
{
	for(int i = m+1; i <= n; ++i)
		Q.insert(i);
}

void ProcessQ()
{
	while(!Q.empty())
	{
		auto first = Q.begin();
		auto station = *first;
		Q.erase(first);
		assert(UnsolvedAdj[station] < 2);
		
		vector<int> rangeValuesBase;
		for(auto adjStation : E[station])
		{
			auto& adjSolutionRange = SolutionRanges[adjStation];
			if(adjSolutionRange.first == 0)
			{
				assert(Q.find(adjStation) != Q.end());
				Q.erase(adjStation);
				--UnsolvedAdj[adjStation];
				Q.insert(adjStation);
				assert(Out[station] == 0);
				Out[station] = adjStation;
			}
			else
			{
				rangeValuesBase.push_back(adjSolutionRange.first);
				rangeValuesBase.push_back(adjSolutionRange.second);
			}
		}
		sort(rangeValuesBase.begin(), rangeValuesBase.end());
		auto rangeSecondI = rangeValuesBase.size() / 2;
		auto rangeFirstI = rangeSecondI - 1;
		auto rangeFirst = rangeValuesBase[rangeFirstI];
		auto rangeSecond = rangeValuesBase[rangeSecondI];
		assert(rangeFirst <= rangeSecond);
		SolutionRanges[station] = {rangeFirst, rangeSecond};
		if(rangeFirst != rangeSecond)
			NoValueStations.push_back(station);
		else
			Values[station] = rangeFirst;
	}
	reverse(NoValueStations.begin(), NoValueStations.end());
}

void SpecifyValues()
{
	for(auto station : NoValueStations)
	{
		auto& stationRange = SolutionRanges[station];
		if(Out[station] == 0)
		{
			Values[station] = stationRange.first;
		}
		else
		{
			auto value = Values[Out[station]];
			if(value > stationRange.second) value = stationRange.second;
			else if(value < stationRange.first) value = stationRange.first;
			Values[station] = value;
		}
	}
}

void CalcAndPrintResult()
{
	ll result = 0ll;
	for(int i = 1; i <= n; ++i)
	{
		assert(Values[i] > 0);
		for(auto adj : E[i])
			result += (ll)abs(Values[i] - Values[adj]);
	}
	printf("%lld", result / 2);
}

inline bool CmpStations::operator () (int s1, int s2)
{
	return UnsolvedAdj[s1] == UnsolvedAdj[s2]
		? s1 < s2
		: UnsolvedAdj[s1] < UnsolvedAdj[s2];
}