#include <bits/stdc++.h>
using namespace std;

#define rep(i, m, n) for(int(i) = (int)(m); i < (int)(n); ++i)
#define rep2(i, m, n) for(int(i) = (int)(n)-1; i >= (int)(m); --i)
#define REP(i, n) rep(i, 0, n)
#define REP2(i, n) rep2(i, 0, n)
#define all(hoge) (hoge).begin(), (hoge).end()
#define en '\n'
using ll = long long;
using ull = unsigned long long;
template <class T>
using vec = vector<T>;
template <class T>
using vvec = vector<vec<T>>;
typedef pair<ll, ll> P;
constexpr long long INF = 1LL << 60;
constexpr int INF_INT = 1 << 25;
constexpr long long MOD = (ll)1e9 + 7;
//constexpr long long MOD = 998244353LL;
using ld = long double;
static const ld pi = 3.141592653589793L;
typedef vector<ll> Array;
typedef vector<Array> Matrix;

template <class T>
inline bool chmin(T &a, T b) {
    if(a > b) {
        a = b;
        return true;
    }
    return false;
}
template <class T>
inline bool chmax(T &a, T b) {
    if(a < b) {
        a = b;
        return true;
    }
    return false;
}

struct Edge {
    ll to, rev;
    long double cap;
    Edge(ll _to, long double _cap, ll _rev) {
        to = _to;
        cap = _cap;
        rev = _rev;
    }
};
using Edges = vector<Edge>;
using Graph = vector<Edges>;

void add_edge(Graph &G, ll from, ll to, long double cap, bool revFlag,
              long double revCap) {
    G[from].push_back(Edge(to, cap, (ll)G[to].size()));
    if(revFlag)
        G[to].push_back(Edge(from, revCap, (ll)G[from].size() - 1));
}

void solve() {

    ll n;
    cin >> n;
    vec<ll> a(n);
    REP(i, n) { cin >> a[i]; }
    Graph g(n);
    REP(i, n - 1) {
        ll u, v;
        cin >> u >> v;
        add_edge(g, --u, --v, 1, true, 1);
    }

    vec<vvec<ll>> dp(n); //i番目の頂点において、j回カットした場合の、kが1ならばコンピュータを含む場合の消費電力の大きさ

    auto dfs = [&](auto &&self, int v, int p) -> void {
        dp[v] = vvec<ll>(1, vec<ll>(2, INF));
        dp[v][0][a[v] < 0] = a[v];

        for(auto e : g[v]) {
            if(e.to == p)
                continue;
            self(self, e.to, v);

            vvec<ll> dp2(dp[v].size() + dp[e.to].size(), vec<ll>(2, INF));
            REP(i, dp[v].size()) {
                REP(j, dp[e.to].size()) {
                    REP(k, 2) {
                        REP(l, 2) {
                            if(dp[v][i][k] == INF or dp[e.to][j][l] == INF)
                                continue;
                            chmin(dp2[i + j][k or l], dp[v][i][k] + dp[e.to][j][l]);
                            if(!l or (l and dp[e.to][j][l] < 0)) {
                                chmin(dp2[i + j + 1][k], dp[v][i][k]); //カットする
                            }
                        }
                    }
                }
            }
            dp[v] = dp2;
        }
    };
    dfs(dfs, 0, -1);

    REP(i, dp[0].size()) {
        REP(j, 2) {
            if(dp[0][i][j] == INF)
                continue;
            if(!j or dp[0][i][j] < 0) {
                cout << i << en;
                return;
            }
        }
    }
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    solve();
    /*
    ll t;
    cin >> t;
    REP(i, t)
    solve();
    */

    return 0;
}


Measured memory_bytes: 573972