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

#define int long long
#define rep(i, n) for (int i = 0; i < (int) (n); i++)
#define reps(i, n) for (int i = 1; i <= (int) (n); i++)
#define all(x) (x).begin(), (x).end()
#define uniq(x) (x).erase(unique(all(x)), (x).end())
#define bit(n) (1LL << (n))
#define cdiv(a, b) (((a) - 1) / (b) + 1)
#define dump(x) cerr << #x " = " << (x) << endl
using vint = vector<int>;
using vvint = vector<vint>;
using pint = pair<int, int>;
using vpint = vector<pint>;
template<typename T> using priority_queue_rev = priority_queue<T, vector<T>, greater<T>>;
constexpr double PI = 3.1415926535897932384626433832795028;
constexpr int DY[9] = {0, 1, 0, -1, 1, 1, -1, -1, 0};
constexpr int DX[9] = {1, 0, -1, 0, 1, -1, -1, 1, 0};
int gcd(int a, int b) {
    while (b) { swap(a %= b, b); }
    return a;
}
int lcm(int a, int b) { return a / gcd(a, b) * b; }
int sgn(int x) { return (x > 0) - (x < 0); }
template<typename T> void fin(T mes) {
    cout << mes << endl;
    exit(0);
}
template<typename T, typename U> bool chmax(T &a, const U &b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
template<typename T, typename U> bool chmin(T &a, const U &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}
template<typename T, typename U> ostream &operator<<(ostream &os, const pair<T, U> &rhs) {
    os << "(" << rhs.first << ", " << rhs.second << ")";
    return os;
}
template<typename T> ostream &operator<<(ostream &os, const vector<T> &rhs) {
    os << "{";
    for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
        os << *itr << (next(itr) != rhs.end() ? ", " : "");
    }
    os << "}";
    return os;
}
struct setup {
    static constexpr int PREC = 20;

    setup() {
        cout << fixed << setprecision(PREC);
        cerr << fixed << setprecision(PREC);
    };
} setup;

int N;
int A[5500];
int U[5500], V[5500];
vint G[5500];
pair<vint, int> dfs(int cur, int par) {
    vint x = {A[cur]};
    int cut = 0;
    for (int to:G[cur]) {
        if (to == par) { continue; }
        pair<vint, int> tmp = dfs(to, cur);
        vint nxt = tmp.first;
        int ccut = tmp.second;
        vint y(x.size() + nxt.size(), LLONG_MAX);
        if (ccut >= 0) { rep(i, x.size()) { y[i + ccut + 1] = x[i]; }}
        rep(i, x.size()) {
            rep(j, nxt.size()) {
                chmin(y[i + j], x[i] + nxt[j]);
                if (nxt[j] < 0) { chmin(y[i + j + 1], x[i]); }
            }
        }
        x = y;
        reps(i, x.size() - 1) { chmin(x[i], x[i - 1]); }
        int pl = INT_MAX;
        for (int i = nxt.size() - 1; i >= 0; i--) { if (nxt[i] < 0) { pl = i; }}
        if (ccut >= 0) { cut += min(ccut, pl + 1); }
        else { cut += pl + 1; }
    }
    if (A[cur] < 0) { cut = -1; }
    return {x, cut};
}

signed main() {
    cin >> N;
    rep(i, N) { cin >> A[i]; }
    rep(i, N - 1) {
        cin >> U[i] >> V[i];
        U[i]--, V[i]--;
        G[U[i]].push_back(V[i]), G[V[i]].push_back(U[i]);
    }
    pair<vint, int> res = dfs(0, -1);
    int ans = N;
    if (A[0] > 0) { ans = res.second; }
    rep(i, res.first.size()) { if (res.first[i] < 0) { chmin(ans, i); }}
    cout << ans << endl;
}

Measured memory_bytes: 5280