#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>

#define ll long long
#define pb push_back
#define f first
#define s second
#define sz(x) (int)(x).size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define ios ios_base::sync_with_stdio(false);cin.tie(NULL)
#define ld long double
#define li __int128

using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>; ///find_by_order(),order_of_key()
template<int D, typename T>struct vec : public vector<vec<D - 1, T>> {template<typename... Args>vec(int n = 0, Args... args) : vector<vec<D - 1, T>>(n, vec<D - 1, T>(args...)) {}};
template<typename T>struct vec<1, T> : public vector<T> {vec(int n = 0, T val = T()) : vector<T>(n, val) {}};
template<class T1,class T2> ostream& operator<<(ostream& os, const pair<T1,T2>& a) { os << '{' << a.f << ", " << a.s << '}'; return os; }
template<class T> ostream& operator<<(ostream& os, const vector<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const deque<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T1,class T2> ostream& operator<<(ostream& os, const map<T1,T2>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
int ri(){int x;scanf("%i",&x);return x;}
void rd(int&x){scanf("%i",&x);}
void rd(long long&x){scanf("%lld",&x);}
void rd(double&x){scanf("%lf",&x);}
void rd(long double&x){scanf("%Lf",&x);}
void rd(string&x){cin>>x;}
void rd(char*x){scanf("%s",x);}
template<typename T1,typename T2>void rd(pair<T1,T2>&x){rd(x.first);rd(x.second);}
template<typename T>void rd(vector<T>&x){for(T&p:x)rd(p);}
template<typename C,typename...T>void rd(C&a,T&...args){rd(a);rd(args...);}
//istream& operator>>(istream& is,__int128& a){string s;is>>s;a=0;int i=0;bool neg=false;if(s[0]=='-')neg=true,i++;for(;i<s.size();i++)a=a*10+s[i]-'0';if(neg)a*=-1;return is;}
//ostream& operator<<(ostream& os,__int128 a){bool neg=false;if(a<0)neg=true,a*=-1;ll high=(a/(__int128)1e18);ll low=(a-(__int128)1e18*high);string res;if(neg)res+='-';if(high>0){res+=to_string(high);string temp=to_string(low);res+=string(18-temp.size(),'0');res+=temp;}else res+=to_string(low);os<<res;return os;}

const int N=1e5+5;
vector<set<pair<ll,int>>> graf(N);
vector<ll> val(N);
vector<int> ord;
vector<int> par(N);
void dfs(int tr,int parent){
	par[tr]=parent;
	for(auto p:graf[tr]){
		if(p.s!=parent){
			dfs(p.s,tr);
		}
	}
	if(graf[tr].count({val[parent],parent})){
		graf[tr].erase({val[parent],parent});
	}
	ord.pb(tr);
}
int main()
{
	int n=ri();
	ll sum=0;
	for(int i=0;i<n;i++){
		val[i]=ri();
		sum+=val[i];
	}
	for(int i=1;i<n;i++){
		int u=ri()-1,v=ri()-1;
		graf[u].insert({val[v],v});
		graf[v].insert({val[u],u});
	}
	dfs(0,0);
	ll ans=0;
	vector<bool> exists(n,1);
	for(auto ind:ord){
		while(1){
			if(sz(graf[ind])==0)
				break;
			if((*graf[ind].rbegin()).f<val[ind])
				break;
			// Worthless move
			if(sz(graf[ind])==1&&sz(graf[(*graf[ind].begin()).s])==0){
				if(n&1){
					ans+=(*graf[ind].rbegin()).f-val[ind];
				}
				else{
					ans+=val[ind]-(*graf[ind].rbegin()).f;
				}
				graf[par[ind]].erase({val[ind],ind});
				exists[ind]=0;
				break;
			}
			
			int koji=(*graf[ind].rbegin()).s,koji2;
			graf[ind].erase({val[koji],koji});
			if(sz(graf[koji])==0||(sz(graf[ind])!=0&&(*graf[koji].rbegin()).f<=(*graf[ind].rbegin()).f)){
				//Taking from root
				koji2=(*graf[ind].rbegin()).s;
				graf[ind].erase({val[koji2],koji2});
			}
			else{
				koji2=(*graf[koji].rbegin()).s;
				graf[koji].erase({val[koji2],koji2});
			}
			/*if(sz(graf[koji])>sz(graf[ind])){
				swap(graf[koji],graf[ind]);
			}
			if(sz(graf[koji2])>sz(graf[ind])){
				swap(graf[koji2],graf[ind]);
			}*/
			for(auto p:graf[koji]){
				graf[ind].insert(p);
			}
			for(auto p:graf[koji2]){
				graf[ind].insert(p);
			}
			if(par[ind]!=ind){
				graf[par[ind]].erase({val[ind],ind});
			}
			val[ind]=val[ind]+val[koji2]-val[koji];
			if(par[ind]!=ind){
				graf[par[ind]].insert({val[ind],ind});
			}
			//cout << ind << ": " << val[ind] << graf[ind] << endl;
		}
	}
	if(exists[0]){
		set<pair<int,int>> options;
		options.insert({val[0],0});
		int v=1;
		while(sz(options)){
			auto tr=*options.rbegin();
			options.erase(tr);
			ans+=tr.f*v;
			v*=-1;
			for(auto p:graf[tr.s]){
				options.insert(p);
			}
		}
	}
	//printf("ans: %lld\n",ans);
	printf("%lld\n",(ans+sum)/2);
	return 0;
}