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

using namespace std;

const int N=500000;
vector<int> t[N];
int nums[N];
int n,m;

struct interval {
    int p;
    int k;
    interval(): p(-1), k(-1) {}
    interval(int pp, int kk): p(pp), k(kk) {}    
} intervals[N];

struct point {
    int x;
    bool p;
    point(int xx, bool pp): x(xx), p(pp) {}
    bool operator<(point a) const { return x < a.x;}
};

interval getInterval(vector<point>&& points) {
    interval ii(-1,-1);
    sort(points.begin(),points.end());
    int finished=0; int x=0;
    int untouched=points.size()/2;
    int i=0;
    while(i<points.size()) {
        int f_prev=finished;
        int u_prev=untouched;
        int x_prev=x;
        x=points[i].x;
        while(i < points.size() && points[i].x==x) {
           if(points[i].p) --untouched;
           else ++finished;
           ++i;
        }
        // pierwszy moment gdy nie oplaca sie juz isc w prawo
        if(untouched < finished) {
            if(u_prev==f_prev) ii.p=x_prev;
            else ii.p=x;
            ii.k=x;
            break;
        }
    }
    return ii;
}

void doIntervals(int v,int parent) {
    if(v < m) { //lisc
        intervals[v].p=nums[v];
        intervals[v].k=nums[v];
        return;
    }

    vector<point> points;
    for(auto w : t[v]) if(w!=parent) {
        //if(v==4) cout << w << endl;
        doIntervals(w,v);
        //if(v==4) cout << intervals[w].p << ", " << intervals[w].k << endl;
        points.push_back(point(intervals[w].p,true));
        points.push_back(point(intervals[w].k,false));
    }
    //if(v==4) { for(auto poi : points) cout << poi.x << ", " << poi.p << "   ";
    //    cout << endl;
    //}
    intervals[v]=getInterval(move(points));
}

void propagateNums(int v,int parent) {
    if(v < m) return;

    if(nums[parent] > intervals[v].k) nums[v]=intervals[v].k;
    else {
        if(nums[parent] < intervals[v].p) nums[v]=intervals[v].p;
        else nums[v]=nums[parent];
    }
    for(auto w : t[v]) if(w!=parent) propagateNums(w,v);
}

long long cost(int v, int parent) {
    if(v < m) return 0;
    long long c=0;

    for(auto w : t[v]) if(w!=parent) {
        c+=cost(w,v);
        c+=abs(nums[v]-nums[w]);
    }
    return c;
}

int main() {
    scanf("%d",&n);
    scanf("%d",&m);

    int v,w;
    for(int i=0; i<n-1; ++i) {
        scanf("%d%d",&v,&w);
        t[v-1].push_back(w-1);
        t[w-1].push_back(v-1);
    }

    fill(nums,nums+N,0);
    for(int i=0; i<m; ++i) scanf("%d",nums+i);

    int root=m;

    //points.clear();
    //points.push_back(point(1,true));
    //points.push_back(point(6,false));
    //points.push_back(point(5,true));
    //points.push_back(point(8,false));
   // points.push_back(point(10,true));
   // points.push_back(point(10,false));
   // points.push_back(point(11,true));
   // points.push_back(point(11,false));
   // points.push_back(point(8,true));
   // points.push_back(point(8,true));
   // points.push_back(point(8,true));
   // points.push_back(point(9,false));
   // points.push_back(point(10,false));
   // points.push_back(point(11,false));

    //interval ii = getInterval();
    //cout << ii.p << ", " << ii.k << endl;
    doIntervals(root,-1);
    //cout << "root(5):" << endl;
    //cout << intervals[root].p << ", " << intervals[root].k << endl;
    //cout << "6:" << endl;
    //cout << intervals[5].p << ", " << intervals[5].k << endl;


    nums[root]=intervals[root].p;
    propagateNums(root,-1);

    //cout << "4:" << nums[4] << endl;
    //cout << "5:" << nums[5] << endl;

    printf("%lld\n",cost(root,-1));

    return 0;
}