/*
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*/
#include <iostream>
#include <complex>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <numeric>
#include <cstring>
#include <ctime>
#include <cstdlib>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <list>
#include <cmath>
#include <bitset>
#include <cassert>
#include <queue>
#include <stack>
#include <deque>
#include <random>
#include <array>
       
        
using namespace std;
template<typename T1, typename T2>inline void chkmin(T1 &x, T2 y) { if (x > y) x = y; }
template<typename T1, typename T2>inline void chkmax(T1 &x, T2 y) { if (x < y) x = y; } 
template<typename T, typename U> inline ostream &operator<< (ostream &_out, const pair<T, U> &_p) { _out << _p.first << ' ' << _p.second; return _out; }
template<typename T, typename U> inline istream &operator>> (istream &_in, pair<T, U> &_p) { _in >> _p.first >> _p.second; return _in; }
template<typename T> inline ostream &operator<< (ostream &_out, const vector<T> &_v) { if (_v.empty()) { return _out; } _out << _v.front(); for (auto _it = ++_v.begin(); _it != _v.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline istream &operator>> (istream &_in, vector<T> &_v) { for (auto &_i : _v) { _in >> _i; } return _in; }
template<typename T> inline ostream &operator<< (ostream &_out, const set<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline ostream &operator<< (ostream &_out, const multiset<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline ostream &operator<< (ostream &_out, const unordered_set<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline ostream &operator<< (ostream &_out, const unordered_multiset<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T, typename U> inline ostream &operator<< (ostream &_out, const map<T, U> &_m) { if (_m.empty()) { return _out; } _out << '(' << _m.begin()->first << ": " << _m.begin()->second << ')'; for (auto _it = ++_m.begin(); _it != _m.end(); ++_it) { _out << ", (" << _it->first << ": " << _it->second << ')'; } return _out; }
template<typename T, typename U> inline ostream &operator<< (ostream &_out, const unordered_map<T, U> &_m) { if (_m.empty()) { return _out; } _out << '(' << _m.begin()->first << ": " << _m.begin()->second << ')'; for (auto _it = ++_m.begin(); _it != _m.end(); ++_it) { _out << ", (" << _it->first << ": " << _it->second << ')'; } return _out; }
#define sz(c) (int)(c).size()
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define left left228
#define right right228
#define rank rank228
#define y1 y1228                                                         
#define read(FILENAME) freopen((FILENAME + ".in").c_str(), "r", stdin)
#define write(FILENAME) freopen((FILENAME + ".out").c_str(), "w", stdout)
#define files(FILENAME) read(FILENAME), write(FILENAME)
#define pb push_back
const string FILENAME = "input";
const int MAXN = 5005;
const long long INF = 1e18;


int n;
long long a[MAXN];
vector<int> g[MAXN];


array<vector<long long>, 2> dfs(int u, int pr = -1) {
    array<vector<long long>, 2> cur;
    if (a[u] < 0) {
        cur[0].pb(INF);
        cur[1].pb(a[u]);
    } else {
        cur[0].pb(a[u]);
        cur[1].pb(a[u]);
    }
    for (auto h: g[u]) {
        if (h == pr) {
            continue;
        }
        auto st = dfs(h, u);
        array<vector<long long>, 2> st1;
        st1[0].resize(sz(cur[0]) - 1 + sz(st[0]) - 1 + 1, INF);
        st1[1].resize(sz(cur[0]) - 1 + sz(st[0]) - 1 + 1, INF);
        for (int i = 0; i < sz(cur[0]); i++) {
            for (int j = 0; j < sz(st[0]); j++) {
                chkmin(st1[0][i + j], cur[0][i] + st[0][j]);
                chkmin(st1[1][i + j], cur[1][i] + st[1][j]);
            }
        }
        cur = st1;
    }
    cur[0].pb(INF);
    cur[1].pb(INF);
    for (int i = 0; i < sz(cur[0]) - 1; i++) {
        if (cur[0][i] < INF) {
            chkmin(cur[0][i + 1], 0LL);
        }
        if (cur[1][i] < 0) {
            chkmin(cur[0][i + 1], 0LL);
        }
    }
    for (int i = 0; i < sz(cur[0]); i++) {
        chkmin(cur[1][i], cur[0][i]);
    }
    return cur;
}


int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    //read(FILENAME);
    cin >> n;
    long long sum = 0;
    for (int i = 0; i < n; i++) {
        cin >> a[i];
        sum += a[i];
    }
    for (int i = 0; i < n - 1; i++) {
        int as, bs;
        cin >> as >> bs;
        as--, bs--;
        g[as].pb(bs);
        g[bs].pb(as);
    }
    if (sum < 0) {
        cout << 0 << endl;
        return 0;
    }
    auto kek = dfs(0);
    int ans = n;
    for (int i = 0; i < sz(kek[0]); i++) {
        if (kek[0][i] < INF || kek[1][i] < 0) {
            chkmin(ans, i + 1);
        }
    }
    cout << ans - 1 << endl;
    return 0;   
}



Measured memory_bytes: 1796