#include "bits/stdc++.h"
using namespace std;

#define FAST ios_base::sync_with_stdio(false); cin.tie(0);
#define pb push_back
#define eb emplace_back
#define ins insert
#define f first
#define s second
#define cbr cerr << "hi\n"
#define mmst(x, v) memset((x), v, sizeof ((x)))
#define siz(x) ll(x.size())
#define all(x) (x).begin(), (x).end()
#define lbd(x,y) (lower_bound(all(x),y)-x.begin())
#define ubd(x,y) (upper_bound(all(x),y)-x.begin())
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());    //can be used by calling rng() or shuffle(A, A+n, rng)
inline long long rand(long long x, long long y) { return (rng() % (y+1-x)) + x; } //inclusivesss
string inline to_string(char c) {string s(1,c);return s;} template<typename T> inline T gcd(T a,T b){ return a==0?llabs(b):gcd(b%a,a); }

typedef long long ll; 
typedef long double ld;
#define FOR(i,s,e) for(ll i=s;i<=ll(e);++i)
#define DEC(i,s,e) for(ll i=s;i>=ll(e);--i)
typedef pair<ll,ll>pi; typedef pair<ll,pi>spi; typedef pair<pi,pi>dpi;

#define LLINF ((long long)1e18)
#define INF int(1e9+1e6)
#define MAXN (5006)
ll n,A[MAXN],dp[MAXN][MAXN],sz[MAXN];// if 0 then max, 1 then min
bitset<MAXN> dp2[MAXN];
vector<int>v[MAXN];
void dfs(ll x,ll p){
	sz[x]=1;
	dp[x][0]=A[x];
	for(auto i:v[x]) if(i^p) dfs(i,x), sz[x]+=sz[i];
	FOR(k,1,sz[x]) dp[x][k]=LLINF;
	ll cur = 1;
	if(A[x]>0)dp2[x][0]=1;
	for(auto i:v[x]) if(i^p) {
		DEC(j,cur+sz[i],0){
			if(dp[x][j]<LLINF) dp[x][j] += dp[i][0];
			dp2[x][j] = dp2[x][j] & dp2[i][0];
			FOR(k,max(j-cur,1ll),min(j,sz[i])){
				dp[x][j]=min(dp[x][j],dp[x][j-k]+dp[i][k]);
				if(dp2[i][k-1]) dp[x][j]=min(dp[x][j],dp[x][j-k]);
				dp2[x][j]=dp2[x][j]|(dp2[x][j-k]&dp2[i][k]);
				if(dp[i][k-1] < 0) dp2[x][j]=dp2[x][j]|dp2[x][j-k];
			}
		}
		cur += sz[i];
	}
}
int main(){
	FAST
	cin>>n;
	FOR(i,1,n)cin>>A[i];
	FOR(i,2,n){
		ll a,b;cin>>a>>b;
		v[a].eb(b),v[b].eb(a);
	}
	dfs(1,1);
	ll ans = n-1;
	FOR(k,0,n-1) if(dp[1][k] < 0) ans = min(ans, k);
	FOR(k,0,n-1) if(dp2[1][k]) ans = min(ans, k);
	cout<<ans<<'\n';
}

