#include <bits/stdc++.h>
#include <ext/pb_ds/priority_queue.hpp>
using namespace std;

#define rep(i, a, b) for (int i = (a); i <= (b); i++)
#define sz(x) (int)(x).size()
using ll = long long;

const int kn = 2e5 + 10;
int n;
ll a[kn], b[kn];
__gnu_pbds::priority_queue<ll> pq[kn];
vector<int> g[kn];

void dfs(int u, int fa) {
    for (int v : g[u]) {
        if (v == fa) continue;
        dfs(v, u);
        pq[u].join(pq[v]);
        b[u] += b[v];
    }
    if (!sz(pq[u]) || a[u] > pq[u].top()) pq[u].push(a[u]);
    else {
        a[u] -= pq[u].top(), pq[u].pop();
        if (sz(pq[u]) && a[u] + pq[u].top() > 0) {
            a[u] += pq[u].top(), pq[u].pop();
            pq[u].push(a[u]);
        } else b[u] += a[u];
    }
}

int main() {
    cin.tie(0)->sync_with_stdio(0);
    cin >> n;
    rep (i, 1, n) cin >> a[i];
    rep (i, 1, n - 1) {
        int u, v;
        cin >> u >> v;
        g[u].push_back(v), g[v].push_back(u);
    }
    dfs(1, 0);
    assert(b[1] <= 0);
    pq[1].push(b[1]);
    ll ans = 0;
    int phase = 0;
    while (sz(pq[1])) {
        if (phase == 0) ans += pq[1].top();
        else ans -= pq[1].top();
        pq[1].pop();
        phase ^= 1;
    }
    cout << ans << "\n";
}