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//Krzysztof Pieprzak
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef unsigned int uint;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int,int> pii;
typedef pair<long long, long long> pll;
typedef vector<pii> vpii;
typedef vector<pll> vpll;

#define Size(x) (int)x.size()
#define VAR(v,n) auto v = (n)
#define FOR(i,a,b) for(VAR(i,a); i < (b); ++i)
#define FORE(i,a,b) for(VAR(i,a); i <= (b); ++i)
#define FORREV(i,a,b) for(VAR(i,b); i >= (a); --i)
#define FORSTEP(i,a,b,step) for(VAR(i,a); i < (b); i += (step))
#define FOREACH(i,c) for(VAR(i,(c).begin()); i != (c).end(); ++i)
#define FOREACHS(i,c,n) for(VAR(i,&(c)[0]); i-(c)<(n); ++i)
#define ALL(x) x.begin(),x.end()
#define CLEAR(t) memset(t, 0, sizeof(t))
#define F first
#define S second
#define MP make_pair
#define PUB push_back
#define POB pop_back
#define pieprzu ios_base::sync_with_stdio(0);

const int    INF = 1000000001;
const double EPS = 10e-9;

const int MAXN = 500000;
int VIS = 1;

struct Pieprzu {
    int rBg;
    int rEd;
    int w;
};

vi t[MAXN+5];
Pieprzu weight[MAXN+5];

int vis[MAXN+5];
queue<int> q;
int doneNeigh[MAXN+5];
bool done[MAXN+5];

pii tab[2*(MAXN+5)];

void inform(int v) {
    done[v] = 1;
    for (auto w : t[v]) {
        ++doneNeigh[w];
        if (Size(t[w]) - doneNeigh[w] <= 1 && !vis[w]) {
            q.push(w);
            vis[w] = 1;
        }
    }
}

void countRange(int v) {
    int vs = 0;
    for (auto w : t[v])
        if (done[w]){
            tab[vs++] = MP(weight[w].rBg, 0);
            tab[vs++] = MP(weight[w].rEd, 1);
        }
    sort(tab, tab+vs);

    int cntClosed = 0;
    int cntWaiting = vs/2;
    bool inRange = false;
    FOR (i, 0, vs) {
        if (tab[i].S == 0)
            --cntWaiting;
        else
            ++cntClosed;

        if (cntClosed == cntWaiting) {
            weight[v].rBg = tab[i].F;
            inRange = true;
        }
        else if (inRange) {
            weight[v].rEd = tab[i].F;
            inRange = false;
            break;
        }
    }
}

void countW(int v, int fatherVal) {
    vis[v] = VIS;
    weight[v].w = max(min(fatherVal, weight[v].rEd), weight[v].rBg);
    for (auto w : t[v])
        if (vis[w] != VIS)
            countW(w, weight[v].w);
}

ll countRes(int v) {
    ll res = 0;
    vis[v] = VIS;
    for (auto w : t[v])
        if (vis[w] != VIS) {
            res += abs(weight[v].w - weight[w].w);
            res += countRes(w);
        }

    return res;
}

void rob(int test) {
    int n, m;
    scanf("%d %d", &n, &m);

    int a, b;
    FOR (i, 1, n) {
        scanf("%d %d", &a, &b);--a;--b;
        t[a].PUB(b);
        t[b].PUB(a);
    }

    FOR (i, 0, m) {
        scanf("%d", &weight[i].w);
        weight[i].rBg = weight[i].rEd = weight[i].w;
        vis[i] = 1;
        inform(i);
    }

    if (m == n) {
        printf("%d\n", abs(weight[0].w - weight[1].w));
        return;
    }

    int root = m;
    while (!q.empty()) {
        root = q.front();q.pop();
        countRange(root);
        inform(root);
    }

    VIS = 2;
    countW(root, -1);

    VIS = 3;
    printf("%lld\n", countRes(root));
}

int main() {
    int test = 1;
    //scanf("%d", &test);

    FORE (i, 1, test) rob(i);

    return 0;
}