#include <bits/stdc++.h>
using namespace std;
#define rep(i, n)  for(long long i=0;i<(long long)(n);i++)
#define REP(i,k,n) for(long long i=k;i<(long long)(n);i++)
#define all(a) a.begin(),a.end()
#define pb push_back
#define eb emplace_back
#define lb(v,k) (lower_bound(all(v),k)-v.begin())
#define ub(v,k) (upper_bound(all(v),k)-v.begin())
#define fi first
#define se second
#define pi M_PI
#define PQ(T) priority_queue<T>
#define SPQ(T) priority_queue<T,vector<T>,greater<T>>
#define dame(a) {out(a);return 0;}
#define decimal cout<<fixed<<setprecision(15);
typedef long long ll;
typedef pair<ll,ll> P;
typedef tuple<ll,ll,ll> PP;
typedef tuple<ll,ll,ll,ll> PPP;
typedef multiset<ll> S;
using vi=vector<ll>;
using vvi=vector<vi>;
using vvvi=vector<vvi>;
using vp=vector<P>;
using vvp=vector<vp>;
using vb=vector<bool>;
using vvb=vector<vb>;
const ll inf=1001001001001001001;
const int INF=1001001001;
const int mod=998244353;
const double eps=1e-10;
template<class T> bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}
template<class T> bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<class T> void out(T a){cout<<a<<'\n';}
template<class T> void outp(T a){cout<<'('<<a.fi<<','<<a.se<<')'<<'\n';}
template<class T> void outvp(T v){rep(i,v.size())cout<<'('<<v[i].fi<<','<<v[i].se<<')';cout<<'\n';}
template<class T> void outvvp(T v){rep(i,v.size())outvp(v[i]);}
template<class T> void outv(T v){rep(i,v.size()){if(i)cout<<' ';cout<<v[i];}cout<<'\n';}
template<class T> void outvv(T v){rep(i,v.size())outv(v[i]);}
template<class T> bool isin(T x,T l,T r){return (l)<=(x)&&(x)<=(r);}
template<class T> void yesno(T b){if(b)out("yes");else out("no");}
template<class T> void YesNo(T b){if(b)out("Yes");else out("No");}
template<class T> void YESNO(T b){if(b)out("YES");else out("NO");}
template<class T> void noyes(T b){if(b)out("no");else out("yes");}
template<class T> void NoYes(T b){if(b)out("No");else out("Yes");}
template<class T> void NOYES(T b){if(b)out("NO");else out("YES");}
void outs(ll a,ll b){if(a>=inf-100)out(b);else out(a);}
ll gcd(ll a,ll b){if(b==0)return a;return gcd(b,a%b);}
ll modpow(ll a,ll b){a%=mod;if(b==0)return 1;if(b&1)return a*modpow(a,b-1)%mod;ll k=modpow(a,b/2);return k*k%mod;}
vi val,sz;
vvi g,dp,dp1;
void dfs(int v,int p){
    sz[v]=1;
    for(ll x:g[v])if(x!=p){
        dfs(x,v);
        sz[v]+=sz[x];
    }
    /*vi sdp(1),sdp1(1);
    sdp[0]=val[v];
    if(val[v]>0)sdp1[0]=1;
    for(ll x:g[v])if(x!=p){
        vi ndp(sdp.size()+sz[x],inf),ndp1(sdp.size()+sz[x]);
        rep(i,sdp.size())rep(j,sz[x]){
            chmin(ndp[i+j],sdp[i]+dp[x][j]);
            if(dp1[x][j]||dp[x][j]<0)chmin(ndp[i+j+1],sdp[i]);
            if(sdp1[i]){
                if(dp[x][j]<0||dp1[x][j])ndp1[i+j+1]=1;
                if(dp1[x][j])ndp1[i+j]=1;
            }
        }
        sdp=ndp;
        sdp1=ndp1;
    }*/
    vi sdp(sz[v]+1,inf),sdp1(sz[v]+1);
    sdp[0]=val[v];
    if(val[v]>0)sdp1[0]=1;
    int cur=0;
    for(ll x:g[v])if(x!=p){
        for(int j=cur;j>=0;j--){
            ll t=sdp[j],t1=sdp1[j];
            sdp[j]=inf;sdp1[j]=0;
            rep(k,sz[x]+1){
                chmin(sdp[j+k],t+dp[x][k]);
                if(dp[x][k]<0||dp1[x][k])chmin(sdp[j+k+1],t);
                if(val[v]>0&&t1){
                    if(dp1[x][k])sdp1[j+k]=1;
                    if(dp[x][k]<0||dp1[x][k])sdp1[j+k+1]=1;
                }
            }
        }
        cur+=sz[x];
    }
    rep(j,sz[v]+1){
        dp[v][j]=sdp[j];
        dp1[v][j]=sdp1[j];
    }
}
int main(){
    ll n;cin>>n;
    val=vi(n);
    sz=vi(n);
    dp1=vvi(n,vi(n+1,inf));
    dp=vvi(n,vi(n+1));
    rep(i,n)cin>>val[i];
    g=vvi(n);
    rep(i,n-1){
        ll a,b;cin>>a>>b;a--;b--;
        g[a].pb(b);
        g[b].pb(a);
    }
    dfs(0,-1);
    ll ans=n;
    rep(i,n)if(dp[0][i]<0||dp1[0][i])chmin(ans,i);
    out(ans);
}

Measured memory_bytes: 392320