#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);
                                            	}
                                            		
                                            
                                            };
                                            

                      
                                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);
                                }
                 
                            
                                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};                                    
}    
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;
                }

                
    			int comb(int nn,int rr){
    				if(rr<0 || rr>nn || nn<0) return 0;
    				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;
                	}
                		inv[ert]=beki(pr[ert],mod-2,mod);
                	for(int i=ert-1;i>=0;i--){
                		inv[i]=inv[i+1]*(i+1)%mod;
                	}
                }
                
              //   cin.tie(0);
    		//	ios::sync_with_stdio(false);
    			//priority_queue<pa3,vector<pa3>,greater<pa3>> pq;            
                 //sort(ve.begin(),ve.end(),greater<int>());
//    mt19937(clock_per_sec);
  //  mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count()) ;
      
       
       
                               //----------------kokomade tenpure------------

int n;
int s[2020]={};
vector<int>G[2200];
vector<int> G2[2200];

int dis[2200];

void dfs(int r,int p,int d){
	dis[r]=d;
	for(auto v:G[r])if(v!=p){
		G2[r].pb(v);
		dfs(v,r,d+1);
	}
}

pa3 memo[2020];


int solve(vector<pa3>&ve){
	int m=ve.size();
	int owari=0;
	int mada=m;
	int ima=0;
	
	int os=0;
	
	vector<pa> V;
	for(auto v:ve){
//		cout<<v.x<<" "<<v.y<<endl;
			V.pb({v.x,0});
			V.pb({v.y,1});
	}
//	cout<<"d"<<endl;
	
	sort(V.begin(),V.end());
	
	int ans=inf*1000000ll;
	
	for(auto v:V){
		if(v.second==0){
			mada--;
			ima++;
		}
		else{
			ima--;
			owari++;
			os+=v.first;
		}
		
		if(mada==0){
			ans=min(ans,v.first-(ima-1)*v.first-os);
		}
	}
	
	return ans;
	
}

void dfs2(int r){
	//cout<<r<<endl;
	for(auto v:G2[r]){
		dfs2(v);
//		cout<<v<<"   "<<memo[v].x<<" "<<memo[v].y<<" "<<memo[v].z<<endl;
	}
	if(G2[r].size()==0){
		memo[r]={0,0,s[r]};
		return;
	}
	
	if(G2[r].size()==1){
		memo[r]=memo[G2[r][0]];
		memo[r].x+=memo[r].z;
		memo[r].y+=memo[r].z;
		if(s[r])memo[r].z++;
		return;
	}
	
	vector<pa3> ve;
	int kosu=s[r];
	int ue=0;
	
	int ki=0;
	for(auto v:G2[r]){
		pa3 z=memo[v];
		z.x+=z.z;
		z.y+=z.z;
		if(z.x%2)ki++;
		kosu+=z.z;
		ue+=z.y;
		ve.pb(z);
	}
	
	int sita=solve(ve);
	if(ki%2==0)sita=max(0ll,sita);
	else sita=max(1ll,sita);
	
	
	memo[r]={sita,ue,kosu};
}


int solve(int r){
	
	for(int i=1;i<=n;i++)G2[i].clear();
	
	dfs(r,r,0);
	
	dfs2(r);
//	cout<<r<<"   "<<memo[r].x<<" "<<memo[r].y<<" "<<memo[r].z<<endl;
	if(memo[r].x!=0) return inf;
	
	
	int zen=0;
	for(int i=1;i<=n;i++)if(s[i])zen+=dis[i];
	
	return zen/2;

	
}

 signed main(){
 	
 
    	       cin.tie(0);
   			ios::sync_with_stdio(false);
cin>>n;
 	
 	string ss;
 	cin>>ss;
 	ss="s"+ss;
 	for(int i=1;i<=n;i++){
 		if(ss[i]=='1')s[i]=1;
 	}
 	for(int i=1;i<n;i++){
 		int y,yy;
 		cin>>y>>yy;
 		G[y].pb(yy);
 		G[yy].pb(y);
 	}
 	int t1=0,t2=0;
 	for(int i=1;i<=n;i++){
 		if(G[i].size()==1) t1++;
 		if(G[i].size()==2) t2++;
 	}
 //cout<<t1<<" "<<t2<<endl;	
 	int ans=inf;
 	for(int i=1;i<=n;i++){
 		int y=solve(i);
 //		cout<<i<<" "<<y<<endl;
 		ans=min(ans,y);
 	}
 	if(ans==inf)cout<<-1<<endl;
 	else cout<<ans<<endl;
 	return 0;
 
  }
 

Measured memory_bytes: 896