#define _CRT_SECURE_NO_WARNINGS
#define _SCL_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cassert>
#include <iostream>
#include <string>
#include <vector>
#include <list>
#include <utility>
#include <algorithm>
#include <functional>
#include <cmath>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <iomanip>
#include <sstream>
#include <bitset>
#include <limits>
#include <numeric>
#include <valarray>
#include <fstream>

using namespace std;
typedef unsigned int uint;
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<LL, LL> PP;
#define REP(i, a, n) for(LL i = (a), i##_max = (n); i < i##_max; ++i)
#define REM(i, a, n) for(LL i = (LL)(n) - 1, i##min = (a); i >= i##min; --i)
#define ALL(arr) (arr).begin(), (arr).end()
#define FLOAT fixed << setprecision(16)
#define SPEEDUP {cin.tie(NULL); ios::sync_with_stdio(false);}
const int INF = 0x3FFFFFFF;
const LL INFLL = 0x3FFFFFFF3FFFFFFF;
const double INFD = 1.0e+308;
const double EPS = 1.0e-9;

void YesNo(bool b) { cout << (b ? "Yes" : "No") << endl; }
void YESNO(bool b) { cout << (b ? "YES" : "NO") << endl; }
template <class T, class U>
istream& operator>>(istream& ist, pair<T, U>& right) { return ist >> right.first >> right.second; }
template <class T, class U>
ostream& operator<<(ostream& ost, const pair<T, U>& right) { return ost << right.first << ' ' << right.second; }
template <class T, class TCompatible, size_t N>
void Fill(T(&dest)[N], const TCompatible& val) { fill(dest, dest + N, val); }
template <class T, class TCompatible, size_t M, size_t N>
void Fill(T(&dest)[M][N], const TCompatible& val) { for (int i = 0; i < M; ++i) Fill(dest[i], val); }
template<class T>
T Compare(T left, T right) { return left > right ? 1 : (left < right ? -1 : 0); }
istream& Ignore(istream& ist) { string s; ist >> s; return ist; }
bool Inside(int i, int j, int h, int w) { return i >= 0 && i < h && j >= 0 && j < w; }
template <class T>
T Next() { T buf; cin >> buf; return buf; }

#ifdef ONLY_MY_ENVIR
#include "IntMod.h"
#include "BinaryMatrix.h"
#include "BIT.h"
#include "Factorization.h"
#include "FlowSolver.h"
#include "Graph.h"
#include "LazySegmentTree.h"
#include "Math.h"
#include "Matrix.h"
#include "MinMax.h"
#include "Position.h"
#include "Range.h"
#include "Rational.h"
#include "SegmentTree.h"
#include "SegmentTree2D.h"
#include "SuffixArray.h"
#include "Tree.h"
#include "UnionFind.h"
#endif

#ifdef __GNUC__
typedef __int128 LLL;
istream& operator>> (istream& ist, __int128& val) { LL tmp;  ist >> tmp; val = tmp; return ist; }
ostream& operator<< (ostream& ost, __int128 val) { LL tmp = val; ost << tmp; return ost; }
#endif

#if 1234567891
#include <array>
#include <random>
#include <unordered_set>
#include <unordered_map>
template<typename T>
using PriorityQ = priority_queue<T, vector<T>, greater<T> >;
// template <class T>
// auto Is(const T& value) { return [value](const auto& comparand) -> bool { return comparand == value; }; }
#endif

int N;
int S[2000];
vector<int> G[2000];

// num, sum
int memo[2000][2001];
PP dist(int from, int prev) {
	PP ret(S[from], 0);
	for (int to : G[from]) {
		if (to == prev) continue;
		PP res = dist(to, from);
		ret.first += res.first;
		ret.second += res.second + res.first;
	}
	memo[from][prev == -1 ? N : prev] = ret.first;
	return ret;
}

PP rec(int from, int prev) {
	PP ret(0, 0);
	for (int to : G[from]) {
		if (to == prev) continue;
		PP res = rec(to, from);
		res.first += memo[to][from];
		res.second += memo[to][from];

		PP a = ret;
		PP b = res;
		if (a > b) swap(a, b);

		int mx;
		int mn;
		if (a.second < b.first) {
			mn = b.first - a.second;
		} else {
			mn = 0;
		}
		mx = a.second + b.second;

		ret = PP(mn, mx);
	}
	return ret;
}

bool ok(int i) {
	PP res = rec(i, -1);
	return res.first == 0;
}

int sub(int i) {
	PP res = dist(i, -1);
	int d = res.second;
	if (d % 2 != 0) return INF;
	
	if (ok(i)) {
		return d / 2;
	} else {
		return INF;
	}
}

int main() {
	cin >> N;
	string s;
	cin >> s;
	REP(i, 0, N) {
		S[i] = s[i] - '0';
	}

	REP(i, 1, N) {
		int a, b;
		cin >> a >> b;
		--a; --b;
		G[a].push_back(b);
		G[b].push_back(a);
	}

	int mn = INF;
	REP(i, 0, N) {
		mn = min(mn, sub(i));
	}
	cout << (mn == INF ? -1 : mn) << endl;
	return 0;
}

Measured memory_bytes: 15744