#include <bits/stdc++.h>

using namespace std;

#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl

typedef long long ll;
#define int ll
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
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; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = 1e18;
const ll MOD = 1000000007;
//const ll MOD = 998244353;
const double pi = 3.14159265358979323846;
#define Sp(p) cout<<setprecision(15)<< fixed<<p<<endl;
int dx[4] = { 1,0, -1,0 }, dy[4] = { 0,1,0,-1 };
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
//#define mp make_pair

const int N = 5010;
vll dp1(N, vl(N, INF));
vl dp2(N, INF);
vii G(N);
vl a(N);
vl sum(N);
vi fu(N);
int n;

void dfs_pre(int now, int par) {
  if (a[now] < 0) fu[now]++;
  sum[now] = a[now];
  rep (i, G[now].size()) {
    if (G[now][i] == par) continue;
    int v = G[now][i];
    dfs_pre(v, now);
    sum[now] += sum[v];
    fu[now] += fu[v];
  }
}

void dfs(int now, int par) {
  int m;
  if (par == -1) {
    m = G[now].size();
  }
  else {
    m = G[now].size() - 1;
  }
  if (m == 0) {
    if (a[now] > 0) {
      dp2[now] = 0;
    }
    else {
      dp2[now] = INF;
    }
    dp1[now][0] = a[now];
    return;
  }
  vll dp(m + 1, vl(n, INF));
  dp[0][0] = a[now];
  int i = 0;
  if (a[now] > 0) dp2[now] = 0;
  rep (aaa, G[now].size()) {
    if (G[now][aaa] == par) continue;
    int v = G[now][aaa];
    dfs(v, now);
    rep (j, n) {
      if (dp[i][j] >= INF / 2) break;
      rep (k, n) {
        if (dp1[v][k] >= INF / 2) break;
        dp[i + 1][j + k] = min(dp[i + 1][j + k], dp[i][j] + dp1[v][k]);
        if (dp1[v][k] < 0) {
          dp[i + 1][j + 1 + k] = min(dp[i + 1][j + 1 + k], dp[i][j]);
        }
      }
      if (dp2[v] < INF / 2) {
        dp[i + 1][j + 1 + dp2[v]] = min(dp[i + 1][j + 1 + dp2[v]], dp[i][j]);
      }
    }
    if (a[now] > 0) {
      ll add = dp2[v];
      rep (j, n) {
        if (dp1[v][j] < 0) {
          add = min(add, j + 1);
          break;
        }
      }
      dp2[now] += add;
    }
    i++;
  }
  rep (i, n) {
    dp1[now][i] = dp[m][i];
  }
  if (a[now] < 0) dp2[now] = INF;
}

signed main() {
  cin >> n;
  rep (i, n) {
    cin >> a[i];
  }
  rep (i, n - 1) {
    int u, v;
    cin >> u >> v;
    u--; v--;
    G[u].push_back(v);
    G[v].push_back(u);
  }
  dfs_pre(0, -1);
  dfs(0, -1);
  ll ans = INF;
  rep (i, n) {
    if (dp1[0][i] < 0) {
      ans = i;
      break;
    }
  }
  ans = min(ans, dp2[0]);
  cout << ans << endl;
}


Measured memory_bytes: 552460