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#include <cstdio>
#include <vector>
#include <algorithm>

int N,M;
std::vector<int> edges[500100];
bool visited[500100];
long long int cost[500100];
int minv[500100];
int maxv[500100];

void calc(int v) {
	visited[v] = true;
	cost[v] = 0;
	std::vector<std::pair<int,int> > childs;
	std::vector<int> nr;

	if (v>M) {
		for (int i=0; i<edges[v].size(); ++i) {
			int n = edges[v][i];
			if (!visited[n]) {
				calc(n);
				nr.push_back(n);
				childs.push_back(std::make_pair(minv[n],-1));
				childs.push_back(std::make_pair(minv[n],0));
				childs.push_back(std::make_pair(maxv[n],-1));
				childs.push_back(std::make_pair(maxv[n],1));
				cost[v]+=cost[n];
			}
		}

		int right = childs.size()/4;
		int left = 0;
		int mindiff = right-left;

		std::sort(childs.begin(), childs.end());
		minv[v] = maxv[v] = childs[0].first;

		for (int i=0;i<childs.size(); ++i) {
			if (childs[i].second == 1) left++;
			else if (childs[i].second == 0) right--;

			if (abs(right-left) < mindiff) {
				mindiff = abs(right-left);
				minv[v] = maxv[v] = childs[i].first;
			} else if (abs(right-left) == mindiff) {
				maxv[v] = childs[i].first;
			}
		}

		for (int i=0;i<nr.size();i++) {
			int n = nr[i];
			if (minv[v] < minv[n]) cost[v] += minv[n]-minv[v];
			else if (minv[v] > maxv[n]) cost[v] += minv[v]-maxv[n];
		}
	}
}

int main() {
	scanf("%d %d",&N,&M);
	for (int i=1;i<N;++i) {
		int a,b;
		scanf("%d %d",&a,&b);
		edges[a].push_back(b);
		edges[b].push_back(a);
		visited[i]=false;
	}

	for (int i=1;i<=M;++i) {
		int w;
		scanf("%d",&w);
		minv[i]=maxv[i]=w;
	}

	calc(N);
	printf("%lld\n",cost[N]);	
	return 0;
}