//注意点
//Tは3つの値を持つ構造
//だがワイルドカードとしても使っている
#include <bits/stdc++.h>
using namespace std;
//@起動時
struct initon {
    initon() {
        cin.tie(0);
        ios::sync_with_stdio(false);
        cout.setf(ios::fixed);
        cout.precision(16);
    };
} __initon;

//@必須構造
struct T {
    int f, s, t;
    T() { f = -1, s = -1, t = -1; }
    T(int f, int s, int t) : f(f), s(s), t(t) {}
    bool operator<(const T &r) const {
        return f != r.f ? f < r.f : s != r.s ? s < r.s : t < r.t;
        //return f != r.f ? f > r.f : s != r.s ? s > r.s : t > r.t; 大きい順
    }
    bool operator>(const T &r) const {
        return f != r.f ? f > r.f : s != r.s ? s > r.s : t > r.t;
        //return f != r.f ? f > r.f : s != r.s ? s > r.s : t > r.t; 小さい順
    }
    int operator[](int i) {
        assert(i < 3);
        return i == 0 ? f : i == 1 ? s : t;
    }
};

//@マクロ省略系 型,構造

#define int int_fast64_t
#define ll long long
#define double long double
#define ull unsigned long long
using dou = double;
using itn = int;
using str = string;
using bo= bool;
using P = pair<int, int>;
#define F first
#define S second
#define vec vector
#define con continue
#define bre break
#define brk break
#define is ==
#define rs resize

//マクロ省略系 コンテナ
using vi = vector<int>;
#define vvi(a, b, c) vec<vi> a(b,vi(c))
using vb = vector<bool>;
#define vvb(a, b, c) vec<vb> a(b,vb(c))
using vs = vector<string>;
#define vvs(a, b, c) vec<vs> a(b,vs(c))
using vl = vector<ll>;
#define vvl(a, b, c) vec<vl> a(b,vl(c))
using vd = vector<double>;
#define vvd(a, b, c) vec<vd> a(b,vd(c))
using vc=vector<char>;
#define vvc(a, b, c) vec<vc> a(b,vc(c))
using vp = vector<P>;
#define vvp(a, b, c) vec<vp> a(b,vp(c))
using vt = vector<T>;
#define vvt(a, b, c) vec<vt> a(b,vt(c))
#define v3i(a, b, c, d) vector<vector<vi>> a(b, vector<vi>(c, vi(d)))
#define v3d(a, b, c, d) vector<vector<vd>> a(b, vector<vd>(c, vd(d)))
#define v3m(a, b, c, d) vector<vector<vm>> a(b, vector<vm>(c, vm(d)))
#define PQ priority_queue<ll, vector<ll>, greater<ll> >
using seti = set<int>;
#define uset unordered_set
#define mset multiset
#define umap unordered_map
#define mmap multimap

//マクロ 繰り返し
#define _overloadrep(_1, _2, _3, name, ...) name
# define _rep(i, n) for(int i = 0; i < n ; i++)
#define repi(i, m, n) for(int i = m; i < n ; i++)
#define rep(...) _overloadrep(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define _rer(i, n) for(int i = n; i >= 0 ; i--)
#define reri(i, m, n) for(int i = m; i >= n ; i--)
#define rer(...) _overloadrep(__VA_ARGS__,reri,_rer,)(__VA_ARGS__)
#define fora(a, b) for(auto&& a : b)
#define forg(gi, ve) if (ve.size())for (int gi = 0, f = ve[gi].from, t = ve[gi].to, c = ve[gi].cost; gi < ve.size(); gi++,f = ve[gi].from, t = ve[gi].to, c = ve[gi].cost)

//マクロ 定数
#define k4 10101
#define k5 101010
#define k6 1010101
#define k7 10101010
const int inf = (int) 1e9 + 100;
const ll linf = (ll) 1e18 + 100;
const double eps = 1e-9;
const int y4[] = {-1, 1, 0, 0};
const int x4[] = {0, 0, -1, 1};
const int y8[] = {0, 1, 0, -1, -1, 1, 1, -1};
const int x8[] = {1, 0, -1, 0, 1, -1, 1, -1};

//マクロ省略形 関数等
#define arsz(a) (sizeof(a)/sizeof(a[0]))
#define sz(a) (a.size())
#define mp make_pair
#define pb push_back
#define pf push_front
#define eb emplace_back
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()

//@拡張系 こう出来るべきというもの

//埋め込み 存在を意識せずに機能を増やされているもの
// 境界チェック付きvector
namespace std_vector_bounds_checking {
    using namespace std;
    template<class T, class A = std::allocator<T>> struct vector : std::vector<T, A> {
        using std::vector<T, A>::vector;
        typename std::vector<T>::reference operator[](typename std::vector<T>::size_type n) {
            return this->at(n);
        }
    };
}
namespace std {
    template<> class hash<std::pair<signed, signed>> {
    public:
        size_t operator()(const std::pair<signed, signed> &x) const {
            return hash<ll>()(((ll) x.first << 32) + x.second);
        }
    };
    template<> class hash<std::pair<ll, ll>> {
    public:
        size_t operator()(const std::pair<ll, ll> &x) const {
            return hash<ll>()(((ll) x.first << 32) + x.second);
        }
    };
}
template<typename T> istream &operator>>(istream &iss, vector<T> &vec) {
    for (T &x: vec) iss >> x;
    return iss;
}
template<typename T> ostream &operator<<(ostream &os, vector <T> &vec) {
    for (int i = 0; i < vec.size(); i++)os << vec[i] << (i + 1 == vec.size() ? "" : " ");
    return os;
}
template<typename V, typename H> void resize(vector<V> &vec, const H head) {  //再帰の終端。 可変長templateの長さが 0 になるとこっちが呼ばれる。
    vec.resize(head);
}
template<typename V, typename H, typename ... T> void resize(vector<V> &vec, const H &head, const T ... tail) {
    vec.resize(head);
    for (auto &v: vec) resize(v, tail...);
}
template<class T> T pop(set<T> &set) {
    T res = *set.begin();
    set.erase(set.find(res));
    return res;
}
template<class T> T pop(mset<T> &set) {
    T res = *set.begin();
    set.erase(set.find(res));
    return res;
}
template<class T> T popBack(set<T> &set) {
    T res = *set.rbegin();
    set.erase(set.find(res));
    return res;
}
template<class T> T popBack(mset<T> &set) {
    T res = *set.rbegin();
    set.erase(set.find(res));
    return res;
}
template<class T> inline void sort(vector<T> &a) { sort(a.begin(), a.end()); };
template<class T> inline void rsort(vector<T> &a) { sort(a.begin(), a.end(), greater<T>()); };
template<class T> inline void sort(vector<T> &a, int len) { sort(a.begin(), a.begin() + len); };
template<class T> inline void rsort(vector<T> &a, int len) { sort(a.begin(), a.begin() + len, greater<T>()); };
template<class T> inline void sort2(vector<vector<T>> &a) { for (int i = 0, n = a.size(); i < n; i++)sort(a[i]); }
template<class T> inline void rsort2(vector<vector<T>> &a) { for (int i = 0, n = a.size(); i < n; i++)rsort(a[i]); }
template<typename A, size_t N, typename T> void fill(A (&a)[N], const T &v) { rep(i, N)a[i] = v; }
template<typename A, size_t N, size_t O, typename T> void fill(A (&a)[N][O], const T &v) { rep(i, N)rep(j, O)a[i][j] = v; }
template<typename A, size_t N, size_t O, size_t P, typename T> void fill(A (&a)[N][O][P], const T &v) { rep(i, N)rep(j, O)rep(k, P)a[i][j][k] = v; }
template<typename A, size_t N, size_t O, size_t P, size_t Q, typename T> void fill(A (&a)[N][O][P][Q], const T &v) { rep(i, N)rep(j, O)rep(k, P)rep(l, Q)a[i][j][k][l] = v; }
template<typename A, size_t N, size_t O, size_t P, size_t Q, size_t R, typename T> void fill(A (&a)[N][O][P][Q][R], const T &v) { rep(i, N)rep(j, O)rep(k, P)rep(l, Q)rep(m, R)a[i][j][k][l][m] = v; }
template<typename A, size_t N, size_t O, size_t P, size_t Q, size_t R, size_t S, typename T> void fill(A (&a)[N][O][P][Q][R][S], const T &v) { rep(i, N)rep(j, O)rep(k, P)rep(l, Q)rep(m, R)rep(n, S)a[i][j][k][l][m][n] = v; }
template<typename V, typename T> void fill(V &x, const T &val) { x = val; }
template<typename V, typename T> void fill(vector<V> &vect, const T &val) { for (auto &v: vect) fill(v, val); }
//@汎用便利関数 入力
template<typename T = int> T in() {
    T x;
    cin >> x;
    return (x);
}
string sin() { return in<string>(); }
double din() { return in<double>(); }
ll lin() { return in<ll>(); }
#define na(a, n) rep(i,n) cin >> a[i];
#define nad(a, n) rep(i,n) cin >> a[i], a[i]--;
#define na3(a, b, c, n) rep(i, n)cin >> a[i] >> b[i] >> c[i];
#define add2(a, b, n) rep(i, n)a.pb(in()),b.pb(in());
#define add2d(a, b, n) rep(i, n)a.pb(in()-1),b.pb(in()-1);
#define add3(a, b, c, n) rep(i, n)a.pb(in()),b.pb(in()),c.pb(in());
#define add3d(a, b, c, n) rep(i, n)a.pb(in()-1),b.pb(in()-1),c.pb(in());
#define na2(a, b, n) rep(i, n)cin >> a[i] >> b[i];
#define nt(a, h, w) rep(hi,h)rep(wi,w) cin >> a[hi][wi];
#define ntd(a, h, w) rep(hi,h)rep(wi,w) cin >> a[hi][wi], a[hi][wi]--;
#define ntp(a, h, w) fill(a,'#');rep(hi,1,h+1)rep(wi,1,w+1) cin >> a[hi][wi];
#define addn(a, n) a.resize(n);na(a,n);
#define addnd(a, n) a.resize(n);na(a,n);rep(i,n)a[i]--;


template<class T> inline void fin(T s) { cout << s << endl, exit(0); }

template<class T> struct edge {
    int from, to;
    T cost;
    int id;
    int type;
    edge(int f, int t, T c = 1, int id = -1, int ty = -1) : from(f), to(t), cost(c), id(id), type(ty) {}
    bool operator<(const edge &b) const { return cost < b.cost; }
    bool operator>(const edge &b) const { return cost > b.cost; }
};

template<typename T> class graph {
protected:
    vector<bool> _used;
public :
    vector<vector<edge<T>>> g;
    vector<edge<T>> edges;
    int n, root = -1;
    graph(int n) : n(n) { g.resize(n), _used.resize(n); }
    void clear() { g.clear(), edges.clear(); }
    void resize(int n) {
        this->n = n;
        g.resize(n);
        _used.resize(n);
    }
    int size() { return g.size(); }
    bool isleaf(int v) {
        assert(root != -1);
        return g[v].size() == 1 && g[v][0].from != root;
    }
    vector<edge<T> > &operator[](int i) { return g[i]; }
    virtual void add(int from, int to, T cost, int ty) = 0;
    virtual bool used(edge<T> &e) = 0;
    virtual bool used(int id) = 0;
    virtual void del(edge<T> &e) = 0;
    virtual void del(int id) = 0;
};

template<class T=int> class undigraph : public graph<T> {
public:
    using graph<T>::g;
    using graph<T>::n;
    using graph<T>::edges;
    using graph<T>::_used;
    undigraph(int n) : graph<T>(n) {
    }
    void add(int f, int t, T cost = 1, int ty = -1) {
        int id = edges.size();
        g[f].emplace_back(f, t, cost, id, ty);
        g[t].emplace_back(t, f, cost, id + 1, ty);
        edges.emplace_back(f, t, cost, id, ty);
        edges.emplace_back(t, f, cost, id + 1, ty);
    }
    void add(edge<T> &e) {
        int f = e.from, t = e.to, ty = e.type;
        T cost = e.cost;
        add(f, t, cost, ty);
    }
    bool used(edge<T> &e) { return _used[e.id]; }
    bool used(int id) { return _used[id]; }
    void del(edge<T> &e) { _used[e.id] = _used[e.id ^ 1] = 1; }
    void del(int id) { _used[id] = _used[id ^ 1] = 1; }
};

template<typename T =ll> class digraph : public graph<T> {
public:
    using graph<T>::g;
    using graph<T>::n;
    using graph<T>::edges;
    using graph<T>::_used;

    digraph(int n) : graph<T>(n) {}
    void add(int f, int t, T cost = 1, int ty = -1) {

        int id = edges.size();
        g[f].emplace_back(f, t, cost, ty, id);
        edges.emplace_back(f, t, cost, ty, id);
    }
    bool used(edge<T> &e) { return _used[e.id]; }
    bool used(int id) { return _used[id]; }
    void del(edge<T> &e) { _used[e.id] = _used[e.id ^ 1] = 1; }
    void del(int id) { _used[id] = _used[id ^ 1] = 1; }
};


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


int n, k, m, h, w, x, y, q;
int cou;
vi a, b, c;
//v3i(dp, 5000, 5001, 2);//コンピューターしかないか
int dp[5000][5001][2],sub[5001][2];
//vvi(sub, 5050, 2);
undigraph<> g(0);
vi es(5050);

void ds(int i, int p) {
    forg(gi, g[i])if (t != p)ds(t, i);
    int sum = 0;
    dp[i][0][a[i] < 0] = a[i];
    forg(gi, g[i]) {
            if (t == p)continue;
            rep(ci, sum + 1) {
                rep(ct, es[t] + 1) {
                    rep(ki, 2) {
                        rep(kt, 2) {
                            //繋ぐ
                            if (dp[i][ci][ki] < linf && dp[t][ct][kt] < linf)
                                chmin(sub[ci + ct][ki || kt], dp[i][ci][ki] + dp[t][ct][kt]);
                            //切る
                            if (dp[t][ct][kt] < 0 || (!kt && dp[t][ct][kt] != linf))
                                chmin(sub[ci + ct + 1][ki], dp[i][ci][ki]);
                        }
                    }
                }
            }
            sum += es[t] + 1;
            rep(j, sum + 1)
                rep(k, 2) {
                    dp[i][j][k] = sub[j][k];
                    sub[j][k] = linf;

                }
        }
    es[i] = sum;
}
signed main() {
    cin >> n;
    addn(a, n);
    g.resize(n);
    rep(i, n - 1) {
        int f, s;
        cin >> f >> s;
        --f, --s;
        g.add(f, s);
    }
    fill(dp, linf);
    fill(sub, linf);
    ds(0, -1);
    rep(c, n)rep(k, 2) {
            if (k) {
                if (dp[0][c][k] < 0)fin(c);
            } else if (dp[0][c][k] != linf)fin(c);
        }

    return 0;
}



Measured memory_bytes: 392856