#include <iostream>
#include <set>

#include <atcoder/dsu>

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    int n;
    std::cin >> n;

    std::vector<std::pair<long long, bool>> sum(n);

    for (int i = 0; i < n; ++i) {
        std::cin >> sum[i].first;
        sum[i].second = true;
    }

    std::vector<std::vector<int>> g(n);
    for (int i = 0; i < n - 1; ++i) {
        int u, v;
        std::cin >> u >> v;
        --u, --v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    std::vector<int> p(n, -1);
    auto dfs = [&](auto dfs, int u) -> void {
        for (int v : g[u]) if (v != p[u]) {
            p[v] = u;
            dfs(dfs, v);
        }
    };
    dfs(dfs, 0);

    std::vector<long long> ans(n);

    auto compare = [&sum](int i, int j) {
        long long dij = sum[i].first - sum[j].first;
        return dij ? dij > 0 : i > j;
    };
    std::set<int, decltype(compare)> st { compare };

    for (int i = 1; i < n; ++i) {
        st.insert(i);
    }

    atcoder::dsu uf(n);

    std::vector<int> root(n);
    for (int i = 0; i < n; ++i) {
        root[i] = i;
    }

    while (not st.empty()) {
        const int u = [&] {
            auto it = st.begin();
            const int u = *it;
            st.erase(it);
            return u;
        }();
        const int v = root[uf.leader(p[u])];

        if (v) st.erase(v);

        if (sum[v].second) {
            sum[v].first -= sum[u].first;
        } else {
            sum[v].first += sum[u].first;
        }
        sum[v].second ^= sum[u].second;

        root[uf.merge(u, v)] = v;

        if (v) st.insert(v);
    }

    std::cout << sum[0].first << '\n';
}