#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<cassert>
#include<complex>
#include<numeric>
using namespace std;

//#define int long long
typedef long long ll;

typedef unsigned long long ul;
typedef unsigned int ui;
constexpr ll mod = 1000000007;
const ll INF = mod * mod;
typedef pair<int, int>P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
#define all(v) (v).begin(),(v).end()
typedef pair<ll, ll> LP;
typedef long double ld;
typedef pair<ld, ld> LDP;
const ld eps = 1e-12;
const ld pi = acos(-1.0);

ll mod_pow(ll x, ll n, ll m) {
	ll res = 1;
	while (n) {
		if (n & 1)res = res * x % m;
		x = x * x % m; n >>= 1;
	}
	return res;
}
struct modint {
	ll n;
	modint() :n(0) { ; }
	modint(ll m) :n(m) {
		if (n >= mod)n %= mod;
		else if (n < 0)n = (n % mod + mod) % mod;
	}
	operator int() { return n; }
};
bool operator==(modint a, modint b) { return a.n == b.n; }
modint operator+=(modint& a, modint b) { a.n += b.n; if (a.n >= mod)a.n -= mod; return a; }
modint operator-=(modint& a, modint b) { a.n -= b.n; if (a.n < 0)a.n += mod; return a; }
modint operator*=(modint& a, modint b) { a.n = ((ll)a.n * b.n) % mod; return a; }
modint operator+(modint a, modint b) { return a += b; }
modint operator-(modint a, modint b) { return a -= b; }
modint operator*(modint a, modint b) { return a *= b; }
modint operator^(modint a, ll n) {
	if (n == 0)return modint(1);
	modint res = (a * a) ^ (n / 2);
	if (n % 2)res = res * a;
	return res;
}

ll inv(ll a, ll p) {
	return (a == 1 ? 1 : (1 - p * inv(p % a, a)) / a + p);
}
modint operator/(modint a, modint b) { return a * modint(inv(b, mod)); }

const int max_n = 1 << 17;
modint fact[max_n], factinv[max_n];
void init_f() {
	fact[0] = modint(1);
	for (int i = 0; i < max_n - 1; i++) {
		fact[i + 1] = fact[i] * modint(i + 1);
	}
	factinv[max_n - 1] = modint(1) / fact[max_n - 1];
	for (int i = max_n - 2; i >= 0; i--) {
		factinv[i] = factinv[i + 1] * modint(i + 1);
	}
}
modint comb(int a, int b) {
	if (a < 0 || b < 0 || a < b)return 0;
	return fact[a] * factinv[b] * factinv[a - b];
}

vector<int> merge(vector<int>& a, vector<int>& b) {
	vector<vector<ll>> dp(a.size()+1, vector<ll>(b.size()+1));
	vector<vector<P>> nex(a.size() + 1, vector<P>(b.size() + 1));
	dp[a.size()][b.size()] = 0;
	//cout << "hello\n";
	//rep(i, a.size())cout << a[i] << " "; cout << "\n";
	//rep(j, b.size())cout << b[j] << " "; cout << "\n";
	per(i, a.size() + 1) {
		per(j, b.size() + 1) {
			int id = (i + j) % 2;
			if (i == a.size() && j == b.size())continue;
			else if (i == a.size()) {
				if (id == 0) {
					dp[i][j] = dp[i][j + 1] + b[j];
					nex[i][j] = { i,j + 1 };
				}
				else {
					dp[i][j] = dp[i][j+1] - b[j];
					nex[i][j] = { i,j+1 };
				}
			}
			else if (j == b.size()) {
				if (id == 0) {
					dp[i][j] = dp[i + 1][j] + a[i];
					nex[i][j] = { i + 1,j };
				}
				else {
					dp[i][j] = dp[i + 1][j] - a[i];
					nex[i][j] = { i + 1,j };
				}
			}
			else {
				if (id == 0) {
					if (dp[i + 1][j]+a[i] < dp[i][j + 1]+b[j]) {
						dp[i][j] = dp[i][j + 1] + b[j];
						nex[i][j] = { i,j + 1 };
					}
					else {
						dp[i][j] = dp[i + 1][j] + a[i];
						nex[i][j] = { i + 1,j };
					}
				}
				else {
					if (dp[i + 1][j]-a[i] > dp[i][j + 1]-b[j]) {
						dp[i][j] = dp[i][j + 1] - b[j];
						nex[i][j] = { i,j + 1 };
					}
					else {
						dp[i][j] = dp[i + 1][j] - a[i];
						nex[i][j] = { i + 1,j };
					}
				}
			}
		}
	}
	vector<int> res;
	int cx = 0, cy = 0;
	while (cx < a.size() || cy < b.size()) {
		int nx = nex[cx][cy].first;
		int ny = nex[cx][cy].second;
		if (cx != nx) {
			res.push_back(a[cx]);
		}
		else {
			res.push_back(b[cy]);
		}
		swap(cx, nx); swap(cy, ny);
	}
	//rep(i, res.size())cout << res[i] << " "; cout << "\n";
	return res;
}

vector<int> G[1000];
int a[1000];
vector<int> dfs(int id, int fr) {
	vector<int> res;
	for (int to : G[id])if (to != fr) {
		vector<int> nex = dfs(to, id);
		res = merge(res, nex);
	}
	res.insert(res.begin(), a[id]);
	return res;
}
void solve() {
	int n; cin >> n; rep(i, n)cin >> a[i];
	rep(i, n - 1) {
		int a, b; cin >>  a >> b; a--; b--;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	vector<int> v = dfs(0, -1);
	ll ans = 0;
	rep(i, n) {
		if (i % 2 == 0)ans += v[i];
		else ans -= v[i];
	}
	cout << ans << "\n";
}




signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	//cout << fixed << setprecision(10);
	//init_f();
	//expr();
	//int t; cin >> t; rep(i, t)
	solve();
	return 0;
}