#include<bits/stdc++.h>
using namespace std;
#define int long long
#define ii pair <int, int>
#define app push_back
#define all(a) a.begin(), a.end()
#define bp __builtin_popcountll
#define ll long long
#define mp make_pair
#define f first
#define s second
#define Time (double)clock()/CLOCKS_PER_SEC
#define debug(x) std::cout << #x << ": " << x << '\n';

const int N = 1e3+7;
vector <int> g[N];
int n, a[N], cnt[N], par[N];
bool del[N];
void dfs(int u, int p) {
    par[u] = p;
    for (int v : g[u]) {
        if (v != p) {
            dfs(v, u);
        }   
    }   
}   

signed main() {
    #ifdef HOME
    freopen("input.txt", "r", stdin);
    #else
    #define endl '\n'
    ios_base::sync_with_stdio(0); cin.tie(0);
    #endif
    cin >> n;
    for (int i = 1; i <= n; ++i)
        cin >> a[i];
    for (int i = 0; i < n - 1; ++i) {
        int u, v;
        cin >> u >> v;
        g[u].app(v); g[v].app(u);
    }       
    dfs(1, 1);
    const int INF = 1e18;
    for (int i = 1; i <= n; ++i)
        cnt[i] = 1;
    for (int t = 0; t < n - 1; ++t) {
        ii mx = mp(-INF, -INF);
        for (int u = 2; u <= n; ++u) {
            if (!del[u]) {
                mx = max(mx, mp(a[u], u));
            }   
        }   
        int u = mx.s;
        for (int i = 2; i <= n; ++i) {
            if (par[i] == u) {
                par[i] = par[u];
            }   
        }   
        del[u] = 1;
        if (cnt[par[u]]&1)
            a[par[u]] -= a[u];
        else            
            a[par[u]] += a[u];
        cnt[par[u]] += cnt[u];
    }   
    cout << a[1] << endl;
}