#include <bits/stdc++.h>

//    #include <boost/multiprecision/cpp_int.hpp>
 #define int long long
 #define inf  1000000007
 #define pa pair<int,int>
 #define ll long long
 #define pal pair<double,double>
 #define ppap pair<pa,int>
  #define PI 3.14159265358979323846
  #define paa pair<int,char>
  #define  mp make_pair
  #define  pb push_back
  #define EPS (1e-10)
                                          
    int dx[8]={0,1,0,-1,1,1,-1,-1};
    int dy[8]={1,0,-1,0,-1,1,1,-1};
                                            using namespace std;
                                   			class pa3{
                                            	public:
                                            	int x;
                                   				int y,z;
                                            	pa3(int x=0,int y=0,int z=0):x(x),y(y),z(z) {}
                                            	bool operator < (const pa3 &p) const{
                                            		if(x!=p.x) return x<p.x;
                                            		if(y!=p.y) return y<p.y;
                                            		 return z<p.z;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                   				bool operator > (const pa3 &p) const{
                                            		if(x!=p.x) return x>p.x;
                                            		if(y!=p.y) return y>p.y;
                                            		 return z>p.z;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const pa3 &p) const{
                                            		return x==p.x && y==p.y && z==p.z;
                                            	}
                                            		bool operator != (const pa3 &p) const{
                                            			return !( x==p.x && y==p.y && z==p.z);
                                            	}
                                            
                                            };
                                            
                                            class pa4{
                                            	public:
                                            	int x;
                                            	int y,z,w;
                                            	pa4(int x=0,int y=0,int z=0,int w=0):x(x),y(y),z(z),w(w) {}
                                            	bool operator < (const pa4 &p) const{
                                            		if(x!=p.x) return x<p.x;
                                            		if(y!=p.y) return y<p.y;
                                            		if(z!=p.z)return z<p.z;
                                            		return w<p.w;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator > (const pa4 &p) const{
                                            		if(x!=p.x) return x>p.x;
                                            		if(y!=p.y) return y>p.y;
                                            		if(z!=p.z)return z>p.z;
                                            		return w>p.w;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const pa4 &p) const{
                                            		return x==p.x && y==p.y && z==p.z &&w==p.w;
                                            	}
                                            		
                                            
                                            };
                                            class pa2{
                                            	public:
                                            	int x,y;
                                            	pa2(int x=0,int y=0):x(x),y(y) {}
                                            	pa2 operator + (pa2 p) {return pa2(x+p.x,y+p.y);}
                                            	pa2 operator - (pa2 p) {return pa2(x-p.x,y-p.y);}
                                            	bool operator < (const pa2 &p) const{
                                            		return y != p.y ? y<p.y: x<p.x;
                                            	}
                                            	bool operator > (const pa2 &p) const{
                                            		return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const pa2 &p) const{
                                            		return abs(x-p.x)==0 && abs(y-p.y)==0;
                                            	}
                                            	bool operator != (const pa2 &p) const{
                                            		return !(abs(x-p.x)==0 && abs(y-p.y)==0);
                                            	}
                                            		
                                            
                                            };
                                            
/*
                                            class Point{
                                            	public:
                                            	double x,y;
                                            	Point(double x=0,double y=0):x(x),y(y) {}
                                            	Point operator + (Point p) {return Point(x+p.x,y+p.y);}
                                            	Point operator - (Point p) {return Point(x-p.x,y-p.y);}
                                            	Point operator * (double a) {return Point(x*a,y*a);}
                                            	Point operator / (double a) {return Point(x/a,y/a);}
                                            	double absv() {return sqrt(norm());}
                                            	double norm() {return x*x+y*y;}
                                            	bool operator < (const Point &p) const{
                                            		return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const Point &p) const{
                                            		return fabs(x-p.x)<EPS && fabs(y-p.y)<EPS;
                                            	}
                                            };
                                            typedef Point Vector;
                                     #define pl pair<int,pas>
                                            struct Segment{
                                            Point p1,p2;
                                            };
                                             double dot(Vector a,Vector b){
                                            	return a.x*b.x+a.y*b.y;
                                            }
                                            double cross(Vector a,Vector b){
                                            	return a.x*b.y-a.y*b.x;
                                            }
                                        
                bool parareru(Point a,Point b,Point c,Point d){
                //	if(abs(cross(a-b,d-c))<EPS)cout<<"dd "<<cross(a-b,d-c)<<endl;
                	return abs(cross(a-b,d-c))<EPS;
                }
                double distance_ls_p(Point a, Point b, Point c) {
                  if ( dot(b-a, c-a) < EPS ) return (c-a).absv();
                  if ( dot(a-b, c-b) < EPS ) return (c-b).absv();
                  return abs(cross(b-a, c-a)) / (b-a).absv();
                }
                bool is_intersected_ls(Segment a,Segment b) {
                	if(a.p1==b.p1||a.p2==b.p1||a.p1==b.p2||a.p2==b.p2) return false;
                	if(parareru((a.p2),(a.p1),(a.p1),(b.p2))&&parareru((a.p2),(a.p1),(a.p1),(b.p1))){
                //		cout<<"sss"<<endl;
                		if(dot(a.p1-b.p1,a.p1-b.p2)<EPS) return true;
                		if(dot(a.p2-b.p1,a.p2-b.p2)<EPS) return true;
                		if(dot(a.p1-b.p1,a.p2-b.p1)<EPS) return true;
                		if(dot(a.p1-b.p2,a.p2-b.p2)<EPS) return true;
                		return false;
                	}
                  else return ( cross(a.p2-a.p1, b.p1-a.p1) * cross(a.p2-a.p1, b.p2-a.p1) < EPS ) && ( cross(b.p2-b.p1, a.p1-b.p1) * cross(b.p2-b.p1, a.p2-b.p1) < EPS );
                }
                 
                double segment_dis(Segment a,Segment b){
                	if(is_intersected_ls(a,b))return 0;
                	double r=distance_ls_p(a.p1, a.p2, b.p1);
                	r=min(r,distance_ls_p(a.p1, a.p2, b.p2));
                	r=min(r,distance_ls_p(b.p1, b.p2, a.p2));
                	r=min(r,distance_ls_p(b.p1, b.p2, a.p1));
                	return r;
                }
                Point intersection_ls(Segment a, Segment b) {
                  Point ba = b.p2-b.p1;
                  double d1 = abs(cross(ba, a.p1-b.p1));
                  double d2 = abs(cross(ba, a.p2-b.p1));
                  double t = d1 / (d1 + d2);
                 
                  return a.p1 + (a.p2-a.p1) * t;
                }
 */                
                                string itos( int i ) {
                                ostringstream s ;
                                s << i ;
                                return s.str() ;
                                }
                                 
                                int gcd(int v,int b){
                                	if(v>b) return gcd(b,v);
                                	if(v==b) return b;
                                	if(b%v==0) return v;
                                	return gcd(v,b%v);
                                }
                 
                                double distans(double x1,double y1,double x2,double y2){
                                	double rr=(x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);
                                	return sqrt(rr);
                                	
                                }
                                int mod;
int extgcd(int a, int b, int &x, int &y) {
    if (b == 0) {
        x = 1;
        y = 0;
        return a;
    }
    int d = extgcd(b, a%b, y, x);
    y -= a/b * x;
    return d;
}
pa operator+(const pa & l,const pa & r) {   
    return {l.first+r.first,l.second+r.second};                                    
}    
                                
                int pr[1200010];
                int inv[1200010];
                
                int beki(int wa,int rr,int warukazu){
                	if(rr==0) return 1%warukazu;
                	if(rr==1) return wa%warukazu;
                	wa%=warukazu;
                	if(rr%2==1) return ((ll)beki(wa,rr-1,warukazu)*(ll)wa)%warukazu;
                	ll zx=beki(wa,rr/2,warukazu);
                	return (zx*zx)%warukazu;
                }
    double bekid(double w,int r){
    	if(r==0) return 1.0;
    	if(r==1) return w;
    	if(r%2) return bekid(w,r-1)*w;
    	double f=bekid(w,r/2);
    	return f*f;
    }
                
    			int comb(int nn,int rr){
    				int r=pr[nn]*inv[rr];
    				r%=mod;
    				r*=inv[nn-rr];
    				r%=mod;
    				return r;
    			}
                
                void gya(int ert){
                	pr[0]=1;
                	for(int i=1;i<=ert;i++){
                		pr[i]=(pr[i-1]*i)%mod;
                	}
                	for(int i=0;i<=ert;i++) inv[i]=beki(pr[i],mod-2,mod);
                	
                }
                
              //   cin.tie(0);
    		//	ios::sync_with_stdio(false);
    			//priority_queue<pa3,vector<pa3>,greater<pa3>> pq;            
                 //sort(ve.begin(),ve.end(),greater<int>());
    
       
       
                               //----------------kokomade tenpure------------


vector<int> G[5010],G2[5010];
int a[5010];

void dfsss(int r,int p){
	for(auto v:G[r])if(v!=p){
		G2[r].pb(v);
		dfsss(v,r);
	}
}
vector<int> ve1[5010],ve2[5010];
int inff=-inf*10000ll;
pair<vector<int>,vector<int>> mer(vector<int> v1,vector<int> v2,vector<int> w1,vector<int> w2){
	//cout<<"her"<<endl;
	
	int n=v1.size();

	int m=v2.size();
	int N=w1.size();
	int M=w2.size();
//	cout<<n<<" "<<m<<" "<<N<<" "<<M<<endl;
		vector<int> t1(max(n+N-1,0ll),-inff),t2(max({n+M,m+N,m+M})-1,-inff);
	for(int i=0;i<n;i++)for(int j=0;j<N;j++)if(v1[i]!=inff && w1[j]!=inff){
		t1[i+j]=min(t1[i+j],v1[i]+w1[j]);
	}
	
	for(int i=0;i<n;i++)for(int j=0;j<M;j++)if(v1[i]!=inff && w2[j]!=inff){
		t2[i+j]=min(t2[i+j],v1[i]+w2[j]);
	}
	
	for(int i=0;i<m;i++)for(int j=0;j<N;j++)if(v2[i]!=inff && w1[j]!=inff){
		t2[i+j]=min(t2[i+j],v2[i]+w1[j]);
	}
	
	for(int i=0;i<m;i++)for(int j=0;j<M;j++)if(v2[i]!=inff && w2[j]!=inff){
		t2[i+j]=min(t2[i+j],v2[i]+w2[j]);
	}
//	cout<<"r"<<endl;
	for(auto &v:t1)if(v==-inff)v*=-1;
	
	for(auto &v:t2)if(v==-inff)v*=-1;
	return {t1,t2};
}

void dfs(int r){
//	cout<<r<<endl;
	for(auto v:G2[r])dfs(v);
	if(G2[r].size()==0){
		if(a[r]>0){
			ve1[r].pb(a[r]);
		}
		else ve2[r].pb(a[r]);
	}
	else{
	
		ve1[r]=ve1[G2[r][0]];
		ve2[r]=ve2[G2[r][0]];
	//	cout<<"dd "<<ve1[r].size()<<" "<<ve2[r].size()<<endl;
		int e=G2[r].size();
		for(int i=1;i<e;i++){
	//		cout<<r<<" dd"<<endl;
			tie(ve1[r],ve2[r])=mer(ve1[r],ve2[r],ve1[G2[r][i]],ve2[G2[r][i]]);
		}
			
		while(ve1[r].size()>ve2[r].size())ve2[r].pb(inff);
		while(ve1[r].size()<ve2[r].size())ve1[r].pb(inff);
		if(a[r]>0){
			for(auto &v:ve1[r])if(v!=inff)v+=a[r];
			for(auto &v:ve2[r])if(v!=inff)v+=a[r];
		}
		else{
			for(auto &v:ve2[r])if(v!=inff)v+=a[r];
			for(int i=0;i<ve1[r].size();i++)if(ve1[r][i]!=inff){
				if(ve2[r][i]==inff) ve2[r][i]=ve1[r][i]+a[r];
				else ve2[r][i]=min(ve2[r][i],ve1[r][i]+a[r]);
			}
			ve1[r].clear();
		}
	}
	
	if(r!=1){
		
		
		for(int i=0;i<ve2[r].size();i++)if(ve2[r][i]<0 && ve2[r][i]!=inff){
			while(ve1[r].size()<i+2)ve1[r].pb(inff);
			ve1[r][i+1]=0ll;
			//else ve1[r][i+1]=max(0ll,ve1[r][i+1]);
		}
		if(ve1[r].size()==0||ve1[r].back()!=inff) ve1[r].pb(inff);
		
		for(int i=ve1[r].size()-2;i>=0;i--)if(ve1[r][i]>0){
		//	cout<<i<<endl;
			ve1[r][i+1]=0ll;
		}
		
		while(ve1[r].size()){
			if(ve1[r].back()==inff) ve1[r].pop_back();
			else break;
		}
		
		while(ve2[r].size()){
			if(ve2[r].back()==inff) ve2[r].pop_back();
			else break;
		}
	}
	/*
	cout<<" ===  "<<r<<endl;
	for(auto v:ve1[r])cout<<v<<" ";
	cout<<endl;
		for(auto v:ve2[r])cout<<v<<" ";
	cout<<endl;
cout<<" ===  "<<endl;
	*/
}

 signed main(){
 	

    	       cin.tie(0);
   			ios::sync_with_stdio(false);
int n;
 	cin>>n;
 	for(int i=1;i<=n;i++)cin>>a[i];
 	for(int i=0;i<n-1;i++){
 		int y,yy;
 		cin>>y>>yy;
 		G[y].pb(yy);
 		G[yy].pb(y);
 	}
 	dfsss(1,1);
 //	cout<<"d"<<endl;
 	dfs(1);
 	int ans=inf;
 	for(int i=0;i<ve2[1].size();i++)if(ve2[1][i]<0)ans=min(ans,i);
 	
 	for(int i=0;i<ve1[1].size();i++)if(ve1[1][i]>=0)ans=min(ans,i);
 	
 	cout<<ans<<endl;
 	return 0;
  }



Measured memory_bytes: 238208