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

#define REP(i,n) for(ll i=0;i<(ll)n;i++)
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define spa << " " <<
#define fi first
#define se second
#define ALL(a)  (a).begin(),(a).end()
#define ALLR(a)  (a).rbegin(),(a).rend()

using ld = long double;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
using pll = pair<long, long>;
using pdd = pair<ld, ld>;

template<typename T> struct V : vector<T> { using vector<T>::vector; };
V() -> V<ll>;
V(size_t) -> V<ll>;
template<typename T> V(size_t, T) -> V<T>;
template<typename T> vector<T> make_vec(size_t n, T a) { return vector<T>(n, a); }
template<typename... Ts> auto make_vec(size_t n, Ts... ts) { return vector<decltype(make_vec(ts...))>(n, make_vec(ts...)); }
template<class S, class T> ostream& operator << (ostream& os, const pair<S, T> v){os << "(" << v.first << ", " << v.second << ")"; return os;}
template<typename T> ostream& operator<<(ostream &os, const vector<T> &v) { for (auto &e : v) os << e << ' '; return os; }
template<class T> ostream& operator<<(ostream& os, const vector<vector<T>> &v){ for(auto &e : v){os << e << "\n";} return os;}
struct fast_ios { fast_ios(){ cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
void fail() { cout << -1 << '\n'; exit(0); }
inline int popcount(const int x) { return __builtin_popcount(x); }
inline int popcount(const ll x) { return __builtin_popcountll(x); }
template<typename T> void debug(vector<vector<T>>&v,ll h,ll w){for(ll i=0;i<h;i++)
{cerr<<v[i][0];for(ll j=1;j<w;j++)cerr spa v[i][j];cerr<<endl;}};
template<typename T> void debug(vector<T>&v,ll n){if(n!=0)cerr<<v[0];
for(ll i=1;i<n;i++)cerr spa v[i];
cerr<<endl;};

const ll INF = (1ll<<60);
// const ld EPS   = 1e-10;
// const ld PI    = acos(-1.0);
const ll mod = (int)1e9 + 7;
//const ll mod = 998244353;
using Graph = V<V<ll>>;

int main(){

    ll N;
    cin >> N;
    V<ll> A(N);
    REP(i, N) cin >> A[i];
    Graph G(N);
    REP(i, N-1){
        ll u, v;
        cin >> u >> v;
        u--, v--;
        G[u].push_back(v);
        G[v].push_back(u);
    }

    V<V<ll>> dp(N);
    V<V<bool>> pos(N);
    V<ll> sz(N, 0);

    auto dfs = [&](auto self, ll now, ll par)->void{
        sz[now] = 1;
        dp[now] = V<ll>(sz[now], INF); 
        pos[now] = V<bool>(sz[now], false); 
        dp[now][0] = A[now];
        pos[now][0] = (A[now]>=0);
        for(auto next: G[now]){
            if(next == par) continue;
            self(self, next, now);
            V<ll> merged(sz[now]+sz[next], INF);
            V<bool> pos_merged(sz[now]+sz[next], false);
            REP(i, sz[now]){
                REP(j, sz[next]){
                    // dump(i)
                    // dump(j)
                    // dump(merged.size())
                    chmin(merged[i+j], dp[now][i]+dp[next][j]);
                    if(pos[now][i] and pos[next][j]) pos_merged[i+j] = true;
                    if(dp[next][j]<0 or pos[next][j]){
                        chmin(merged[i+j+1], dp[now][i]);
                        if(pos[now][i]) pos_merged[i+j+1] = true;
                    }
                }
            }
            sz[now] += sz[next];
            dp[now] = merged;
            pos[now] = pos_merged;
        }
    };

    dfs(dfs, 0, -1);

    ll res = (1ll<<60);

    REP(i, N){
        if(dp[0][i]<0) chmin(res, i);
        if(pos[0][i]) chmin(res, i);
    }

    cout << res << endl;

    return 0;
}

Measured memory_bytes: 127164