//#define _GLIBCXX_DEBUG
#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0; i<(n); i++)
#define rng(i,l,r) for(int i=(l); i<(r); i++)
#define rrep(i,n) for(int i=(n)-1; i>=0; i--)
#define each(i,x) for(auto i:x)
#define all(x) x.begin(),x.end()
using ll=long long;
#define fi first
#define se second

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n;cin>>n;
    vector<ll> a(n);
    rep(i,n)cin>>a[i];
    ll sa=0;
    each(i,a)sa+=i;
    vector<vector<int>> tree(n);
    rep(i,n-1){
        int u,v;cin>>u>>v;
        tree[u-1].push_back(v-1);
        tree[v-1].push_back(u-1);
    }
    vector<int> order={0};
    vector<int> par(n,-2);
    par[0]=-1;
    rep(i,n){
        int p=order[i];
        each(j,tree[p]){
            if(par[j]==-2){
                par[j]=p;
                order.push_back(j);
            }
        }
    }
    reverse(all(order));
    vector<priority_queue<ll>> pq(n);
    ll ans=0;
    each(i,order){
        pair<int,int> mx={-1,-1};
        each(j,tree[i]){
            if(par[i]==j)continue;
            mx=max(mx,{pq[j].size(),j});
        }
        if(mx.se!=-1){
            swap(pq[mx.se],pq[i]);
        }
        each(j,tree[i]){
            if(par[i]==j||j==mx.se)continue;
            while(!pq[j].empty()){
                pq[i].push(pq[j].top());
                pq[j].pop();
            }
        }
        bool flg=true;
        while(!pq[i].empty()&&pq[i].top()>a[i]){
            if(pq[i].size()==1){
                flg=false;
                if(n%2==1){
                    ans-=a[i];
                    ans+=pq[i].top();
                }
                else{
                    ans+=a[i];
                    ans-=pq[i].top();
                }
                pq[i].pop();
            }
            else{
                a[i]-=pq[i].top();
                pq[i].pop();
                a[i]+=pq[i].top();
                pq[i].pop();
            }
        }
        if(flg)pq[i].push(a[i]);
    }
    int sign=1;
    while(!pq[0].empty()){
        ans+=sign*pq[0].top();
        pq[0].pop();
        sign*=-1;
    }
    cout<<ans<<"\n";
}