#pragma region Macros
#pragma GCC optimize("O3")

#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define rep2(i,a,b) for(ll i=a;i<=b;++i)
#define rep(i,n) for(ll i=0;i<n;++i)
#define rep3(i,a,b) for(ll i=a;i>=b;--i)
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pb push_back
#define eb emplace_back
#define vi vector<int>
#define vec vector<int>
#define vll vector<ll>
#define vpi vector<pii>
#define vpll vector<pll>
#define overload2(_1,_2,name,...) name
#define vv(a,b) vector<vector<int>>(a,vector<int>(b))
#define vv2(a,b,c) vector<vector<int>>(a,vector<int>(b,c))
#define vvl(a,b) vector<vector<ll>>(a,vector<ll>(b))
#define vvl2(a,b,c) vector<vector<ll>>(a,vector<ll>(b,c))
#define vvv(a,b,c) vector<vv(b,c)>(a)
#define vvv2(a,b,c,d) vector<vv(b,c,d)>(a)
#define vvvl(a,b,c) vector<vvl(b,c)>(a)
#define vvvl2(a,b,c,d) vector<vvl(b,c,d)>(a)
#define fi first
#define se second
#define all(c) begin(c),end(c)
#define ios ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
#define lb(c,x) distance((c).begin(),lower_bound(all(c),(x)))
#define ub(c,x) distance((c).begin(),upper_bound(all(c),(x)))
using namespace std;
template<class T> using pq = priority_queue<T>;
template<class T> using pqg = priority_queue<T,vector<T>,greater<T>>;
#define INT(...) int __VA_ARGS__;IN(__VA_ARGS__)
#define LL(...) ll __VA_ARGS__;IN(__VA_ARGS__)
#define ULL(...) ull __VA_ARGS__;IN(__VA_ARGS__)
#define STR(...) string __VA_ARGS__;IN(__VA_ARGS__)
#define CHR(...) char __VA_ARGS__;IN(__VA_ARGS__)
#define DBL(...) double __VA_ARGS__;IN(__VA_ARGS__)
#define LD(...) ld __VA_ARGS__;IN(__VA_ARGS__)
#define VEC(type,name,size) vector<type> name(size);IN(name)
#define VV(type,name,h,w) vector<vector<type>>name(h,vector<type>(w));IN(name)
int scan(){ return getchar(); }
void scan(int& a){ cin>>a; }
void scan(long long& a){ cin>>a; }
void scan(char &a){cin>>a;}
void scan(double &a){ cin>>a; }
void scan(long double& a){ cin>>a; }
void scan(char a[]){ scanf("%s", a); }
void scan(string& a){ cin >> a; }
template<class T> void scan(vector<T>&);
template<class T, size_t size> void scan(array<T, size>&);
template<class T, class L> void scan(pair<T, L>&);
template<class T, size_t size> void scan(T(&)[size]);
template<class T> void scan(vector<T>& a){ for(auto& i : a) scan(i); }
template<class T> void scan(deque<T>& a){ for(auto& i : a) scan(i); }
template<class T, size_t size> void scan(array<T, size>& a){ for(auto& i : a) scan(i); }
template<class T, class L> void scan(pair<T, L>& p){ scan(p.first); scan(p.second); }
template<class T, size_t size> void scan(T (&a)[size]){ for(auto& i : a) scan(i); }
template<class T> void scan(T& a){ cin >> a; }
void IN(){}
template <class Head, class... Tail> void IN(Head& head, Tail&... tail){ scan(head); IN(tail...); }
string stin() {string s;cin>>s;return s;}
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;}
vi iota(int n){vi a(n);iota(all(a),0);return a;}
template<class T> void UNIQUE(vector<T> &x){sort(all(x));x.erase(unique(all(x)),x.end());}
int in() {int x;cin>>x;return x;}
ll lin() {unsigned long long x;cin>>x;return x;}
void print(){putchar(' ');}
void print(bool a){cout<<a;}
void print(int a){cout<<a;}
void print(long long a){cout<<a;}
void print(char a){cout<<a;}
void print(string &a){cout<<a;}
void print(double a){cout<<a;}
template<class T> void print(const vector<T>&);
template<class T, size_t size> void print(const array<T, size>&);
template<class T, class L> void print(const pair<T, L>& p);
template<class T, size_t size> void print(const T (&)[size]);
template<class T> void print(const vector<T>& a){ if(a.empty()) return; print(a[0]); for(auto i = a.begin(); ++i != a.end(); ){ cout<<" "; print(*i); } cout<<endl;}
template<class T> void print(const deque<T>& a){ if(a.empty()) return; print(a[0]); for(auto i = a.begin(); ++i != a.end(); ){ cout<<" "; print(*i); } }
template<class T, size_t size> void print(const array<T, size>& a){ print(a[0]); for(auto i = a.begin(); ++i != a.end(); ){ cout<<" "; print(*i); } }
template<class T, class L> void print(const pair<T, L>& p){ cout<<'(';print(p.first); cout<<","; print(p.second);cout<<')'; }
template<class T, size_t size> void print(const T (&a)[size]){ print(a[0]); for(auto i = a; ++i != end(a); ){ cout<<" "; print(*i); } }
template<class T> void print(const T& a){ cout << a; }
int out(){ putchar('\n'); return 0; }
template<class T> int out(const T& t){ print(t); putchar('\n'); return 0; }
template<class Head, class... Tail> int out(const Head& head, const Tail&... tail){ print(head); putchar(' '); out(tail...); return 0; }
ll gcd(ll a, ll b){ while(b){ ll c = b; b = a % b; a = c; } return a; }
ll lcm(ll a, ll b){ if(!a || !b) return 0; return a * b / gcd(a, b); }
vector<pll> factor(ll x){ vector<pll> ans; for(ll i = 2; i * i <= x; i++) if(x % i == 0){ ans.push_back({i, 1}); while((x /= i) % i == 0) ans.back().second++; } if(x != 1) ans.push_back({x, 1}); return ans; }
vector<int> divisor(int x){ vector<int> ans; for(int i=1;i*i<=x;i++)if(x%i==0){ans.pb(i);if(i*i!=x)ans.pb(x/i);} return ans;}
int popcount(ll x){return __builtin_popcountll(x);}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int rnd(int n){return uniform_int_distribution<int>(0, n)(rng);}
#define endl '\n'

#ifdef _LOCAL
    #undef endl
    #define debug(x) cout<<#x<<": ";print(x);cout<<endl;
    void err(){}
    template<class T> void err(const T& t){ print(t);  cout<<" ";}
    template<class Head, class... Tail> void err(const Head& head, const Tail&... tail){ print(head); putchar(' '); out(tail...); }
#else
    #define debug(x)
    template<class... T> void err(const T&...){}
#endif
#pragma endregion


template< typename T >
struct edge{
    int from, to;
    T cost;
    edge(int to,T cost) : from(-1), to(to), cost(cost){}
    edge(int from,int to,T cost) : from(from), to(to), cost(cost){}
    edge &operator=(const int &x) {
        to = x;
        return *this;
    }
    operator int() const{ return to;}
};

template< typename T >
using Edges = vector< edge< T > >;
template< typename T >
using WeightedTree = vector< Edges<T>>;
using tree = vector< vector<int> >;

tree make(int n,int offset = 1){
    tree res(n);
    for(int i = 0;i < n-1; i++){
        int a,b; cin >> a >> b;
        a -= offset,b -= offset;
        res[a].emplace_back(b);
        res[b].emplace_back(a);
    }
    return res;
}
template< typename T >
WeightedTree<T> make2(int n, int offset = 1){
    WeightedTree<T> res(n);
    for(int i = 0;i < n-1 ; i++){
        int a,b ; cin >> a >> b;
        a -= offset, b -= offset;
        T c; cin >> c;
        res[a].emplace_back(b,c);
        res[b].emplace_back(a,c);
    }
    return res;
}


signed main(){
    ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);cout<<fixed<<setprecision(15);
    INT(n);
    VEC(ll,a,n);
    auto g = make(n);
    auto dp1 = vector<vll>(n);
    // plus only
    auto dp2 = vector<ll>(n,0);
    // to cut all
    auto dp3 = vector<ll>(n);

    auto merge = [&](vll &x, vll &y){
        int a = x.size() , b = y.size();
        vll res(a+b-1,1e15);
        rep(i,a)rep(j,b)chmin(res[i+j],x[i] + y[j]);
        swap(x,res);
    };
    constexpr ll INF = 1e16;
    auto dfs = [&](auto &&f,int x,int p) -> void{
        dp1[x].pb(a[x]);
        for(auto e:g[x])if(e!=p)f(f,e,x);
        for(auto e:g[x]){
            if(e==p)continue;
            vll nxt(dp1[x].size() + max(dp1[e].size()-1,(size_t)dp3[e]),INF);
            rep(i,dp1[x].size())rep(j,dp1[e].size()) chmin(nxt[i+j],dp1[x][i] + dp1[e][j]);
            rep(i,dp1[x].size()) chmin(nxt[i+dp3[e]],dp1[x][i]);
            swap(nxt,dp1[x]);
        }

        if( a[x] > 0 )
        for(auto e:g[x]){
            if(e==p)continue;
            dp2[x] += dp2[e];
        }
        else dp2[x] = INF;
        dp3[x] = INF;
        rep(i,dp1[x].size()) if(dp1[x][i] < 0) chmin(dp3[x],i + 1);
        chmin(dp3[x],dp2[x] + 1);
        chmin(dp2[x],dp3[x]);
    };
    dfs(dfs,0,-1);
    cout << dp3[0] - 1 << endl;  
            
            

    
    
}           


Measured memory_bytes: 59648