#line 2 "/Users/kaage/Desktop/ProgrammingWorkspace/library/other/template.hpp"
#define _CRT_SECURE_NO_WARNINGS
#pragma target("avx2")
#pragma optimize("O3")
#pragma optimize("unroll-loops")
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <memory>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <string.h>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#define rep(i,n) for(int i=0;i<(n);i++)
#define REP(i,n) for(int i=1;i<=(n);i++)
#define all(V) V.begin(),V.end()
typedef long long lint;
typedef unsigned long long ulint;
typedef std::pair<int, int> P;
typedef std::pair<lint, lint> LP;
constexpr int INF = INT_MAX/2;
constexpr lint LINF = LLONG_MAX/2;
constexpr double eps = DBL_EPSILON;
constexpr double PI=3.141592653589793238462643383279;
template<class T>
class prique :public std::priority_queue<T, std::vector<T>, std::greater<T>> {};
template <class T, class U>
inline bool chmax(T& lhs, const U& rhs) {
	if (lhs < rhs) {
		lhs = rhs;
		return 1;
	}
	return 0;
}
template <class T, class U>
inline bool chmin(T& lhs, const U& rhs) {
	if (lhs > rhs) {
		lhs = rhs;
		return 1;
	}
	return 0;
}
inline lint gcd(lint a, lint b) {
	while (b) {
		lint c = a;
		a = b; b = c % b;
	}
	return a;
}
inline lint lcm(lint a, lint b) {
	return a / gcd(a, b) * b;
}
bool isprime(lint n) {
	if (n == 1)return false;
	for (int i = 2; i * i <= n; i++) {
		if (n % i == 0)return false;
	}
	return true;
}
template<typename T>
T mypow(T a, lint b) {
	T res(1);
	while(b){
		if(b&1)res*=a;
		a*=a;
		b>>=1;
	}
	return res;
}
lint modpow(lint a, lint b, lint m) {
	lint res(1);
	while(b){
		if(b&1){
			res*=a;res%=m;
		}
		a*=a;a%=m;
		b>>=1;
	}
	return res;
}
template<typename T>
void printArray(std::vector<T>& vec) {
	rep(i, vec.size()){
		std::cout << vec[i];
		std::cout<<(i==(int)vec.size()-1?"\n":" ");
	}
}
template<typename T>
void printArray(T l, T r) {
	T rprev = std::prev(r);
	for (T i = l; i != rprev; i++) {
		std::cout << *i << " ";
	}
	std::cout << *rprev << std::endl;
}
LP extGcd(lint a,lint b) {
	if(b==0)return {1,0};
	LP s=extGcd(b,a%b);
	std::swap(s.first,s.second);
	s.second-=a/b*s.first;
	return s;
}
LP ChineseRem(const lint& b1,const lint& m1,const lint& b2,const lint& m2) {
	LP sol=extGcd(m1,m2);
	lint p=sol.first,q=sol.second;
	lint tmp=(b2-b1)*p%m2;
	lint r=(b1+m1*tmp+m1*m2)%(m1*m2);
	return std::make_pair(r,m1*m2);
}
#line 2 "main.cpp"
int n,c[2010],d[2010];
std::string s;
std::vector<int> vec[2010];
bool used[2010];
template<typename F>
inline constexpr decltype(auto) fix(F&& f){
	return [f=std::forward<F>(f)](auto&&... args){
		return f(f,std::forward<decltype(args)>(args)...);
	};
}
int main(){
	std::cin>>n>>s;
	rep(i,n-1){
		int a,b;
		std::cin>>a>>b;
		a--;b--;
		vec[a].push_back(b);
		vec[b].push_back(a);
	}
	int ans=INF;
	rep(i,n){
		std::fill(used,used+n,false);
		std::fill(c,c+n,0);
		fix([&](auto f,int node)->void{
			used[node]=true;
			if(s[node]=='1')c[node]++;
			for(int j:vec[node]){
				if(!used[j]){
					f(f,j);
					c[node]+=c[j];
				}
			}
		})(i);
		std::fill(used,used+n,false);
		P cnt=fix([&](auto f,int node)->P{
			used[node]=true;
			P res={0,0};
			std::vector<P> v;
			int maxsum=0;
			for(int j:vec[node]){
				if(!used[j]){
					P k=f(f,j);
					maxsum+=k.second;
					v.push_back(k);
				}
			}
			std::sort(all(v),std::greater<P>());
			if(!v.empty()){
				if(maxsum-v[0].second<v[0].first)res={v[0].first-(maxsum-v[0].second),maxsum};
				else res={0,maxsum};
			}
			if(node!=i){
				res.first+=c[node];res.second+=c[node];
			}
			return res;
		})(i);
		if(cnt.first==0&&cnt.second%2==0)chmin(ans,cnt.second);
	}
	if(ans!=INF)std::cout<<ans/2<<std::endl;
	else std::cout<<-1<<std::endl;
	return 0;
}

Measured memory_bytes: 3968