using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using SB = System.Text.StringBuilder;
//using System.Threading.Tasks;
//using System.Text.RegularExpressions;
//using System.Globalization;
//using System.Diagnostics;
using static System.Console;
using System.Numerics;
using static System.Math;
using pair = Pair<int, int>;

class Program
{
    static void Main()
    {
        //SetOut(new StreamWriter(OpenStandardOutput()) { AutoFlush = false });
        new Program().solve();
        Out.Flush();
    }
    readonly Scanner cin = new Scanner();
    readonly int[] dd = { 0, 1, 0, -1, 0 }; //→↓←↑
    readonly int mod = 1000000007;
    readonly int dom = 998244353;
    bool chmax<T>(ref T a, T b) where T : IComparable<T> { if (a.CompareTo(b) < 0) { a = b; return true; } return false; }
    bool chmin<T>(ref T a, T b) where T : IComparable<T> { if (b.CompareTo(a) < 0) { a = b; return true; } return false; }

    int N;
    List<int>[] G;
    long[] A;

    long[,] dp, pd; //vの部分木の最小値、後者はすべて正
    long[] sdp, spd;
    int[] num; //vの部分木の頂点数


    void dfs(int u, int pa)
    {
        num[u] = 1;
        foreach (var v in G[u])
        {
            if (v == pa) continue;
            dfs(v, u);
            num[u] += num[v];

        }
        for (int j = 0; j < num[u]; j++)
        {
            sdp[j] = (long)1e14;
            spd[j] = -1;
        }

        sdp[0] = A[u];
        if (A[u] > 0) spd[0] = A[u];

        int curnum = 1; //見たノードの数の和
        foreach (var v in G[u])
        {
            if (v == pa) continue;
            for (int j = curnum - 1; j >= 0; j--)
            {
                var p = sdp[j];
                var q = spd[j];
                sdp[j] = (long)1e14;
                spd[j] = -1;
                for (int k = 0; k < num[v]; k++)
                {
                    chmin(ref sdp[j + k], p + dp[v, k]);
                    if (dp[v, k] < 0 || pd[v, k] > 0) chmin(ref sdp[j + k + 1], p);

                    if (q > 0)
                    {
                        if (pd[v, k] > 0)
                        {
                            if (spd[j + k] < 0) spd[j + k] = q + pd[v, k];
                            else chmin(ref spd[j + k], q + pd[v, k]);
                        }
                        if (dp[v, k] < 0 || pd[v, k] > 0)
                        {
                            if (spd[j + k + 1] < 0) spd[j + k + 1] = q;
                            else chmin(ref spd[j + k + 1], q);
                        }
                    }
                }
            }

            curnum += num[v];
        }

        for (int j = 0; j < num[u]; j++)
        {
            dp[u, j] = sdp[j];
            pd[u, j] = spd[j];
        }
        //Write($"i={u}: "); sdp.join();
        //Write($"i={u}: "); spd.join();
    }

    void solve()
    {
        N = cin.nextint;
        A = cin.scanlong;

        G = Enumerable.Range(0, N).Select(i => new List<int>()).ToArray();
        for (int i = 0; i < N - 1; i++)
        {
            int a = cin.nextint - 1;
            int b = cin.nextint - 1;
            G[a].Add(b);
            G[b].Add(a);
        }

        pd = new long[N, N];
        dp = new long[N, N];
        sdp = new long[N];
        spd = new long[N];
        for (int i = 0; i < N; i++)
        {
            for (int j = 0; j < N; j++)
            {
                dp[i, j] = (long)1e14;
                pd[i, j] = -1;
            }
        }
        num = new int[N];

        dfs(0, -1);

        for (int i = 0; i < N; i++)
        {
            if (dp[0, i] < 0 || pd[0, i] > 0)
            {
                WriteLine(i);
                return;
            }
        }

    }

}


static class Ex
{
    public static void join<T>(this IEnumerable<T> values, string sep = " ") => WriteLine(string.Join(sep, values));
    public static string concat<T>(this IEnumerable<T> values) => string.Concat(values);
    public static string reverse(this string s) { var t = s.ToCharArray(); Array.Reverse(t); return t.concat(); }

    public static int lower_bound<T>(this IList<T> arr, T val) where T : IComparable<T>
    {
        int low = 0, high = arr.Count;
        int mid;
        while (low < high)
        {
            mid = ((high - low) >> 1) + low;
            if (arr[mid].CompareTo(val) < 0) low = mid + 1;
            else high = mid;
        }
        return low;
    }
    public static int upper_bound<T>(this IList<T> arr, T val) where T : IComparable<T>
    {
        int low = 0, high = arr.Count;
        int mid;
        while (low < high)
        {
            mid = ((high - low) >> 1) + low;
            if (arr[mid].CompareTo(val) <= 0) low = mid + 1;
            else high = mid;
        }
        return low;
    }
}

class Pair<T, U> : IComparable<Pair<T, U>> where T : IComparable<T> where U : IComparable<U>
{
    public T f; public U s;
    public Pair(T f, U s) { this.f = f; this.s = s; }
    public int CompareTo(Pair<T, U> a) => f.CompareTo(a.f) != 0 ? f.CompareTo(a.f) : s.CompareTo(a.s);
    public override string ToString() => $"{f} {s}";
}

class Scanner
{
    string[] s; int i;
    readonly char[] cs = new char[] { ' ' };
    public Scanner() { s = new string[0]; i = 0; }
    public string[] scan => ReadLine().Split();
    public int[] scanint => Array.ConvertAll(scan, int.Parse);
    public long[] scanlong => Array.ConvertAll(scan, long.Parse);
    public double[] scandouble => Array.ConvertAll(scan, double.Parse);
    public string next
    {
        get
        {
            if (i < s.Length) return s[i++];
            string st = ReadLine();
            while (st == "") st = ReadLine();
            s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
            i = 0;
            return next;
        }
    }
    public int nextint => int.Parse(next);
    public long nextlong => long.Parse(next);
    public double nextdouble => double.Parse(next);
}


Measured memory_bytes: 405968