#include <bits/stdc++.h>
using namespace std;
using lint = long long;
const lint mod = 1e6 + 3;
#define all(x) (x).begin(), (x).end()
#define bitcount(n) __builtin_popcountl((lint)(n))
#define fcout cout << fixed << setprecision(15)
#define highest(x) (63 - __builtin_clzl(x))
template<class T> inline void YES(T condition){ if(condition) cout << "YES" << endl; else cout << "NO" << endl; }
template<class T> inline void Yes(T condition){ if(condition) cout << "Yes" << endl; else cout << "No" << endl; }
template<class T = string, class U = char>int character_count(T text, U character){ int ans = 0; for(U i: text){ ans += (i == character); } return ans; }
lint power(lint base, lint exponent, lint module){ if(exponent % 2){ return power(base, exponent - 1, module) * base % module; }else if(exponent){ lint root_ans = power(base, exponent / 2, module); return root_ans * root_ans % module; }else{ return 1; }}
struct position{ int y, x; }; position mv[4] = {{0, -1}, {1, 0}, {0, 1}, {-1, 0}}; // double euclidean(position first, position second){ return sqrt((second.x - first.x) * (second.x - first.x) + (second.y - first.y) * (second.y - first.y)); }
template<class T, class U> string to_string(pair<T, U> x){ return to_string(x.first) + "," + to_string(x.second); } string to_string(string x){ return x; }
template<class itr> void array_output(itr start, itr goal){ string ans; for(auto i = start; i != goal; i++) ans += to_string(*i) + " "; if(!ans.empty()) ans.pop_back(); cout << ans << endl; }
template<class itr> void cins(itr first, itr last){ for(auto i = first; i != last; i++){ cin >> (*i); } }
template<class T> T gcd(T a, T b){ if(a && b){ return gcd(min(a, b), max(a, b) % min(a, b)); }else{ return a; }} template<class T> T lcm(T a, T b){ return a / gcd(a, b) * b; }
struct combination{ vector<lint> fact, inv; combination(int sz) : fact(sz + 1), inv(sz + 1){ fact[0] = 1; for(int i = 1; i <= sz; i++){ fact[i] = fact[i - 1] * i % mod; } inv[sz] = power(fact[sz], mod - 2, mod); for(int i = sz - 1; i >= 0; i--){ inv[i] = inv[i + 1] * (i + 1) % mod; } } lint C(int p, int q) const{ if(q < 0 || p < q) return 0; return (fact[p] * inv[q] % mod * inv[p - q] % mod); } };
template<class itr> bool next_sequence(itr first, itr last, int max_bound){ itr now = last; while(now != first){ now--; (*now)++; if((*now) == max_bound){ (*now) = 0; }else{ return true; } } return false; }

int N;
string S;
vector<vector<int>> roads;

struct data{
    lint size, piece, dist, climb;
};

data dfs(int now, int back){
    vector<data> child;
    for(int i: roads[now]){
        if(i != back){
            child.push_back(dfs(i, now));
            child.back().dist += child.back().piece;
        }
    }
    lint size_sum = 1, piece_sum = S[now], dist_sum = 0, dist_max = -1e9, dist_max_index = -1;
    for(int i = 0; i < child.size(); i++){
        size_sum += child[i].size;
        piece_sum += child[i].piece;
        dist_sum += child[i].dist;
        if(dist_max < child[i].dist){
            dist_max = child[i].dist;
            dist_max_index = i;
        }
    }
    if(child.empty()){
        return {size_sum, piece_sum, dist_sum, 0};
    }
    lint other_dist = dist_sum - dist_max;
    lint climb = min(dist_sum / 2, other_dist + child[dist_max_index].climb);
    return {size_sum, piece_sum, dist_sum, climb};
}

signed main(){
    cin >> N >> S;
    roads.resize(N);
    for(int i = 0; i < N - 1; i++){
        int a, b;
        cin >> a >> b;
        a--, b--;
        roads[a].push_back(b);
        roads[b].push_back(a);
    }
    for(int i = 0; i < N; i++){
        S[i] -= '0';
    }
    lint ans = 1e18;
    for(int i = 0; i < N; i++){
        auto ret = dfs(i, -1);
        if(ret.climb * 2 == ret.dist){
            ans = min(ans, ret.climb);
        }
    }
    if(ans >= 1e17){
        cout << -1 << endl;
    }else{
        cout << ans << endl;
    }
}


Measured memory_bytes: 640