#include <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <ctime>
#include <cstring>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <numeric>
#include <utility>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <unordered_map>
using namespace std;

#define REP(i, s) for (int i = 0; i < s; ++i)
#define ALL(v) (v.begin(), v.end())
#define COUT(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << endl
#define EACH(i, s) for (__typeof__((s).begin()) i = (s).begin(); i != (s).end(); ++i)

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<class T1, class T2> ostream& operator << (ostream &s, pair<T1,T2> P)
{ return s << '<' << P.first << ", " << P.second << '>'; }
template<class T> ostream& operator << (ostream &s, vector<T> P)
{ for (int i = 0; i < P.size(); ++i) { if (i > 0) { s << " "; } s << P[i]; } return s; }
template<class T> ostream& operator << (ostream &s, vector<vector<T> > P)
{ for (int i = 0; i < P.size(); ++i) { s << endl << P[i]; } return s << endl; }
template<class T> ostream& operator << (ostream &s, set<T> P)
{ EACH(it, P) { s << "<" << *it << "> "; } return s << endl; }
template<class T1, class T2> ostream& operator << (ostream &s, map<T1,T2> P)
{ EACH(it, P) { s << "<" << it->first << "->" << it->second << "> "; } return s << endl; }

const long long INF = 1LL<<60;
const int MAX = 5100;

int N;
vector<long long> A;
vector<vector<int> > G;

int num[MAX];
long long dp[MAX][MAX][2]; // vの部分木、vを含めず何個か、(全部正かどうか)
long long sdp[2][MAX][2];

void rec(int v, int p) {
    int numc = 0;
    num[v] = 1;
    for (auto ch : G[v]) {
        if (ch == p) continue;
        rec(ch, v);
        ++numc;
        num[v] += num[ch];
    }
    
    for (int i = 0; i < 2; ++i) for (int j = 0; j <= num[v]; ++j)
        sdp[i][j][0] = sdp[i][j][1] = INF;
    
    sdp[0][0][0] = A[v];
    if (A[v] > 0) sdp[0][0][1] = A[v];
    
    int i = 0;
    for (auto ch : G[v]) {
        if (ch == p) continue;
        for (int j = 0; j <= num[v]; ++j) {
            if (sdp[i%2][j][0] > INF/2) break;
            for (int k = 0; k <= num[ch] && j+k <= num[v]; ++k) {
                chmin(sdp[(i+1)%2][j+k][0], sdp[i%2][j][0] + dp[ch][k][0]);
                chmin(sdp[(i+1)%2][j+k][0], sdp[i%2][j][0] + dp[ch][k][1]);
                if (dp[ch][k][0] < 0) chmin(sdp[(i+1)%2][j+k+1][0], sdp[i%2][j][0]);
                if (dp[ch][k][1] < INF/2) chmin(sdp[(i+1)%2][j+k+1][0], sdp[i%2][j][0]);
                if (A[v] > 0) {
                    chmin(sdp[(i+1)%2][j+k][1], sdp[i%2][j][1] + dp[ch][k][1]);
                    if (dp[ch][k][0] < 0) chmin(sdp[(i+1)%2][j+k+1][1], sdp[i%2][j][1]);
                    if (dp[ch][k][1] < INF/2) chmin(sdp[(i+1)%2][j+k+1][1], sdp[i%2][j][1]);
                }
            }
        }
        for (int j = 0; j <= num[v]; ++j) sdp[i%2][j][0] = sdp[i%2][j][1] = INF;
        ++i;
    }
    for (int j = 0; j <= num[v]; ++j) {
        dp[v][j][0] = sdp[numc%2][j][0];
        dp[v][j][1] = sdp[numc%2][j][1];
        
        //cout << v << ", " << j << ": " << make_pair(dp[v][j][0], dp[v][j][1]) << endl;
    }
}

int main() {
    while (cin >> N) {
        A.resize(N);
        for (int i = 0; i < N; ++i) cin >> A[i];
        G.assign(N, vector<int>());
        for (int i = 0; i < N-1; ++i) {
            int u, v; cin >> u >> v; --u, --v;
            G[u].push_back(v);
            G[v].push_back(u);
        }
        for (int i = 0; i < MAX; ++i) for (int j = 0; j < MAX; ++j)
            dp[i][j][0] = dp[i][j][1] = INF;
        rec(0, -1);
        int res = N;
        for (int i = 0; i <= N; ++i) {
            if (dp[0][i][0] < 0) chmin(res, i);
            if (dp[0][i][1] < INF/2) chmin(res, i);
        }
        cout << res << endl;
    }
}
























Measured memory_bytes: 407808