#include <bits/stdc++.h>
#define ll long long
#define INF (1LL << 60)
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)(n);++i)
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;--i)
#define srep(i,s,t) for(int i=(int)(s);i<(int)(t);++i)
#define each(a,b) for(auto& (a): (b))
#define all(v) (v).begin(),(v).end()
#define len(v) (int)(v).size()
#define zip(v) sort(all(v)),v.erase(unique(all(v)),v.end())
#define cmx(x,y) x=max(x,y)
#define cmn(x,y) x=min(x,y)
#define fi first
#define se second
#define pb push_back
#define show(x) cout<<#x<<" = "<<(x)<<endl
#define sar(a,n) cout<<#a<<":";rep(pachico,n)cout<<" "<<a[pachico];cout<<endl

using namespace std;

template<typename S,typename T>auto&operator<<(ostream&o,pair<S,T>p){return o<<"{"<<p.fi<<","<<p.se<<"}";}
template<typename T>auto&operator<<(ostream&o,set<T>s){for(auto&e:s)o<<e<<" ";return o;}
template<typename S,typename T,typename U>
auto&operator<<(ostream&o,priority_queue<S,T,U>q){while(!q.empty())o<<q.top()<<" ",q.pop();return o;}
template<typename K,typename T>auto&operator<<(ostream&o,map<K,T>&m){for(auto&e:m)o<<e<<" ";return o;}
template<typename T>auto&operator<<(ostream&o,vector<T>v){for(auto&e:v)o<<e<<" ";return o;}
void ashow(){cout<<endl;}template<typename T,typename...A>void ashow(T t,A...a){cout<<t<<" ";ashow(a...);}
template<typename S,typename T,typename U>
struct TRI{S fi;T se;U th;TRI(){}TRI(S f,T s,U t):fi(f),se(s),th(t){}};
template<typename S,typename T,typename U>
auto&operator<<(ostream&o,TRI<S,T,U>&t){return o<<"{"<<t.fi<<","<<t.se<<","<<t.th<<"}";}

typedef pair<int, int> P;
typedef pair<ll, ll> pll;
typedef TRI<int, int, int> tri;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
typedef vector<P> vp;
typedef vector<double> vd;
typedef vector<string> vs;

const int MAX_N = 5005;

vector<int> G[MAX_N];
ll dp[MAX_N][MAX_N][2][2];
ll a[MAX_N];

int dfs(int u, int p)
{
    int nw = 0;
    dp[u][0][0][0] = dp[u][0][1][0] = INF;
    if(a[u] < 0) dp[u][0][1][0] = a[u];
    else dp[u][0][0][0] = a[u];
    for(int v : G[u]){
        if(v != p){
            int st = dfs(v, u);
            rep(j,nw+st+1){
                rep(k,2){
                    dp[u][j][k][1] = INF;
                }
            }
            rrep(i,nw+1){
                rep(j,st){
                    // 0 の場合
                    cmn(dp[u][i+j][0][1], dp[u][i][0][0]+dp[v][j][0][0]);
                    // 1 の場合
                    cmn(dp[u][i+j][1][1], dp[u][i][0][0]+dp[v][j][1][0]);
                    cmn(dp[u][i+j][1][1], dp[u][i][1][0]+dp[v][j][0][0]);
                    cmn(dp[u][i+j][1][1], dp[u][i][1][0]+dp[v][j][1][0]);
                    // 切る場合
                    if(dp[v][j][0][0] <= INF/10 || dp[v][j][1][0] < 0){
                        cmn(dp[u][i+j+1][0][1], dp[u][i][0][0]);
                        cmn(dp[u][i+j+1][1][1], dp[u][i][1][0]);
                    }
                }
            }
            nw += st;
            rep(j,nw+1){
                rep(k,2){
                    dp[u][j][k][0] = dp[u][j][k][1];
                }
            }
        }
    }
    return nw+1;
}

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    rep(i,n){
        cin >> a[i];
    }
    rep(i,n-1){
        int u,v;
        cin >> u >> v;
        G[u-1].pb(v-1), G[v-1].pb(u-1);
    }
    dfs(0, -1);
    int ans = n-1;
    rep(i,n){
        if(dp[0][i][0][0] <= INF/10) cmn(ans, i);
        if(dp[0][i][1][0] < 0) cmn(ans, i);
    }
    cout << ans << "\n";
    return 0;
}


Measured memory_bytes: 782464