#ifdef LOCAL111
	#define _GLIBCXX_DEBUG
#else
	#pragma GCC optimize ("O3")
	#define NDEBUG
#endif
// #define _USE_MATH_DEFINES
#include <bits/stdc++.h>
const int INF = 1e9;
using namespace std;
template<typename T, typename U> ostream& operator<< (ostream& os, const pair<T,U>& p) { os << '(' << p.first << ' ' << p.second << ')'; return os; }

#define endl '\n'
#define ALL(a)  (a).begin(),(a).end()
#define SZ(a) int((a).size())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n)  FOR(i,0,n)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#ifdef LOCAL111
	#define DEBUG(x) cout<<#x<<": "<<(x)<<endl
	template<typename T> void dpite(T a, T b){ for(T ite = a; ite != b; ite++) cout << (ite == a ? "" : " ") << *ite; cout << endl;}
#else
	#define DEBUG(x) true
	template<typename T> void dpite(T a, T b){ return; }
#endif
#define F first
#define S second
#define SNP string::npos
#define WRC(hoge) cout << "Case #" << (hoge)+1 << ": "
template<typename T> void pite(T a, T b){ for(T ite = a; ite != b; ite++) cout << (ite == a ? "" : " ") << *ite; cout << endl;}
template<typename T> bool chmax(T& a, T b){if(a < b){a = b; return true;} return false;}
template<typename T> bool chmin(T& a, T b){if(a > b){a = b; return true;} return false;}

template<typename T>
vector<T> make_v(size_t a){return vector<T>(a);}

template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts){
  return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}

template<typename T,typename U,typename... V>
typename enable_if<is_same<T, U>::value!=0>::type
fill_v(U &u,const V... v){u=U(v...);}

template<typename T,typename U,typename... V>
typename enable_if<is_same<T, U>::value==0>::type
fill_v(U &u,const V... v){
  for(auto &e:u) fill_v<T>(e,v...);
}

const array<int, 4> dx = {0, 1, 0, -1};
const array<int, 4> dy = {1, 0, -1, 0};


typedef long long int LL;
typedef unsigned long long ULL;
typedef pair<int,int> P;

void ios_init(){
	//cout.setf(ios::fixed);
	//cout.precision(12);
#ifdef LOCAL111
	return;
#endif
	ios::sync_with_stdio(false); cin.tie(0);
}

// 検証しなおしたい

//library
typedef long long cost_t;

class Edge {
public:
	int to = -1;
	cost_t cost = -1;
	
	Edge(){
	}

	Edge(int x,cost_t y){
		to = x;
		cost = y;
	}

	// Edge(int x, int y, cost_t z){
	// 	// from = x;
	// 	to = y;
	// 	cost = z;
	// }

	// Edge(int x, int y, int r, cost_t z){
	// 	// from = x;
	// 	to = y;
	// 	cost = z;
	// 	// rev = r;
	// }

	bool operator< (const Edge& x) const {
		if(cost != x.cost) return cost < x.cost;
		return to < x.to;
	}

	bool operator> (const Edge& x) const {
		if(cost != x.cost) return cost > x.cost;
		return to > x.to;
	}
};

class Graph {
private:
	typedef vector<Edge> Edges;
	//const long long int INF = (long long)1e18;
	vector<Edges> v; 
	int n;
public:
	Graph(int x){
		n = x;
		v = vector<Edges>(x);
	}

	Graph(){}

	Edges& operator[](int x){
		return v[x];
	}

	const Edges& operator[](int x) const {
		return v[x];
	}

	int size() const {
		return n;
	}

	void add_edge(int from, const Edge &e){
		v[from].push_back(e);
	}

	void add_edge(int from, int to, cost_t cost = -1){
		add_edge(from,Edge(to,cost));
	}

	// void add_edge(int from, int to, cost_t cost = -1, int rev = -1){
	// 	add_edge(from,Edge(from,to,rev,cost));
	// }

	void add_uedge(int from, int to, cost_t cost = -1){
		add_edge(from,to,cost);
		add_edge(to,from,cost);
	}
};

int main()
{
	ios_init();
	int n;
	// GraphVizualizer viz;
	while(cin >> n) {
		string s;
		cin >> s;
		Graph g(n);
		REP(i, n - 1) {
			int a, b;
			cin >> a >> b;
			a--; b--;
			g.add_uedge(a, b);
		}
		// viz(g);
		vector<LL> dsum(n);
		vector<LL> dp(n);
		vector<LL> cnt(n);
		function<void(int, int, int)> set_dep = [&](int v, int pre, int d) {
			LL sum = 0;
			LL ma = 0;
			int mai = -1;
			for(auto&& e : g[v]) {
				if(e.to == pre) {
					continue;
				}
				set_dep(e.to, v, d + 1);
			}
			DEBUG(v);
			for(auto&& e : g[v]) {
				if(e.to == pre) {
					continue;
				}
				sum += dsum[e.to];
				cnt[v] += cnt[e.to];
				// DEBUG(dsum[e.to] + cnt[e.to]);
				if(chmax(ma, dsum[e.to] + cnt[e.to])) {
					mai = e.to;
				}
			}
			dsum[v] = sum + cnt[v];
			if(s[v] == '1') {
				cnt[v]++;
			}
			
			if(mai != -1) {
				if((ma - dp[mai]) * 2 <= dsum[v]) {
					dp[v] = dsum[v] / 2;
				} else {
					dp[v] = dsum[v] - (ma - dp[mai]);
				}
			}

		};

		LL INF = 1e17;
		LL ans = INF;
		REP(r, n) {
			fill(ALL(dsum), 0);
			fill(ALL(dp), 0);
			fill(ALL(cnt), 0);
			set_dep(r, -1, 0);
			DEBUG(r);
			dpite(ALL(dsum));
			dpite(ALL(dp));
			dpite(ALL(cnt));
			DEBUG(dsum[r]);
			DEBUG(dp[r]);
			if(dsum[r] == dp[r] * 2) {
				chmin(ans, dp[r]);
			}
			DEBUG(ans);
		}
		if(ans == INF) {
			cout << -1 << endl;
		} else {
			cout << ans << endl;
		}


		// LL ans = INF;
		// REP(r, n) {
		// 	DEBUG(r);
		// 	set_dep(r, -1, 0);
		// 	dpite(ALL(dp));
		// 	dpite(ALL(cnt));
		// 	LL sum = 0;
		// 	LL ma = 0;
		// 	for(auto&& e : g[r]) {
		// 		sum += dp[e.to];
		// 		chmax(ma, dp[e.to]);
		// 	}
		// 	if(sum % 2 == 0 && ma <= sum / 2) {
		// 		chmin(ans, sum / 2);
		// 	}
		// }
		// if(ans == INF) {
		// 	cout << -1 << endl;
		// } else {
		// 	cout << ans << endl;
		// }
	}
	return 0;
}


Measured memory_bytes: 768