#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#pragma GCC optimize("unroll-loops")
//#pragma warning(disable : 4996)

#ifdef _MSC_VER
#include <intrin.h>
#define __builtin_popcount __popcnt
#define __builtin_popcountll __popcnt64
#endif

#include <limits.h>
#include <math.h>
#include <time.h>

#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <complex>
#include <cstdio>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPR(i, n) for (int i = n - 1; i >= 0; --i)
#define FOR(i, m, n) for (int i = m; i < n; ++i)
#define FORR(i, m, n) for (int i = m - 1; i >= n; --i)
#define SORT(v, n) sort(v, v + n);
#define VSORT(v) sort(v.begin(), v.end());
#define REVERSE(v, n) reverse(v, v + n);
#define VREVERSE(v) reverse(v.begin(), v.end())
#define ll long long
#define print(x) cout << (x) << '\n'
#define pe(x) cout << (x) << " "
#define DEBUG(x) cout << #x << ": " << x << endl
#define lb(v, n) lower_bound(v.begin(), v.end(), (n))
#define ub(v, n) upper_bound(v.begin(), v.end(), (n))
//#define int long long
#define double long double
#define all(x) (x).begin(), (x).end()
#define print_space(v) REP(i, v.size()) cout << v[i] << ((i == v.size() - 1) ? "\n" : " ")
template <typename T1, typename T2> inline void chmin(T1& a, T2 b) {
	if (a > b) a = b;
}
template <typename T1, typename T2> inline void chmax(T1& a, T2 b) {
	if (a < b) a = b;
}
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
typedef array<int, 3> arr3;
std::random_device rd;
std::mt19937 mt(rd());
constexpr ll MOD = 998244353;
constexpr int MAX = 500050;
const double pi = acos(-1);
constexpr double EPS = 1e-8;
constexpr ll LINF = 1e18 + 1;
constexpr int INF = 1e9 + 1;

vector<int>G[5001];
int siz[5001];
int par[5001];
int calc_size(int n) {
	//print(n);
	int res = 1;
	for (auto nxt : G[n]) {
		if (nxt == par[n])continue;
		par[nxt] = n;
		res += calc_size(nxt);
	}
	return siz[n] = res;
}

//ll dp[5001][2][5001];
ll dp[5010][2][5020];
bool vis[5050];
ll ndp[2][5050];
void rec(int i) {
	if (vis[i])return;
	vis[i] = true;
	int sz = 1;
	for (auto nxt : G[i]) {
		if (nxt == par[i])continue;
		rec(nxt);
		int nsz = siz[nxt];
		REP(j, 2)REP(k, sz + nsz + 1)ndp[j][k] = LINF;
		int mn = INF;
		REP(j, 2)REP(k, nsz)if ((j == 0 && dp[nxt][j][k] < LINF) || dp[nxt][j][k] < 0)chmin(mn, k);
		//cut
		REP(j, 2)REP(k, sz + nsz + 1) {
			if (k + mn > 5001)break;
			chmin(ndp[j][k + mn+1],dp[i][j][k]);
		}
		//merge
		REP(j, 2)REP(k, sz + 1)REP(nj, 2)REP(nk, nsz + 1) {
			chmin(ndp[j | nj][k + nk], dp[i][j][k] + dp[nxt][nj][nk]);
		}
		REP(j, 2)REP(k, sz + nsz + 1)dp[i][j][k] = ndp[j][k];
		sz += nsz;
	}
	return;
}


void solve() {
	int N; cin >> N;
	vector<int>A(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);
	}

	calc_size(0);

	REP(i, N + 1)REP(j, 2)REP(k, N + 1)dp[i][j][k] = LINF;
	REP(i, N) {
		if (A[i] < 0)dp[i][1][0] = A[i];
		else dp[i][0][0] = A[i];
	}
	rec(0);
	ll ans = INF;
	REP(j, 2)REP(k, N) {
		if ((j == 0&&dp[0][j][k]<LINF) || dp[0][j][k] < 0) {
			chmin(ans, k);
		}
	}
	print(ans);
}





signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	mt.seed((int)(time(0)));
	//int q;
	//cin >> q;
	//while (q--)
	solve();
}



Measured memory_bytes: 394624