// #define DEBUGGING
#include <bits/stdc++.h>
#define endl '\n'
#define ALL(V) (V).begin(), (V).end()
#define ALLR(V) (V).rbegin(), (V).rend()
using ll = std::int64_t;
using ull = std::uint64_t;
using PLL = std::pair<ll, ll>;
using TLL = std::tuple<ll, ll, ll>;
template <typename T> using V = std::vector<T>;
template <typename T> using VV = V<V<T>>;
template <typename T> const T& var_min(const T &t) { return t; }
template <typename T> const T& var_max(const T &t) { return t; }
template <typename T, typename... Tail> const T& var_min(const T &t, const Tail&... tail) { return std::min(t, var_min(tail...)); }
template <typename T, typename... Tail> const T& var_max(const T &t, const Tail&... tail) { return std::max(t, var_max(tail...)); }
template <typename T, typename... Tail> void chmin(T &t, const Tail&... tail) { t = var_min(t, tail...); }
template <typename T, typename... Tail> void chmax(T &t, const Tail&... tail) { t = var_max(t, tail...); }
template <typename T> const T& clamp(const T &t, const T &low, const T &high) { return std::max(low, std::min(high, t)); }
template <typename T> void chclamp(T &t, const T &low, const T &high) { return t = clamp(t, low, high); }
namespace init__ { struct InitIO { InitIO() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); std::cout << std::fixed << std::setprecision(30); } } init_io; }
#define mv_rec make_v(init, tail...)
template <typename T> T make_v(T init) { return init; }
template <typename T, typename... Tail> auto make_v(T init, size_t s, Tail... tail) { return V<decltype(mv_rec)>(s, mv_rec); }
#undef mv_rec
using namespace std;

#ifdef DEBUGGING
#include "../../debug/debug.cpp"
#else
#define DEBUG(...) 0
#define DEBUG_SEPARATOR_LINE 0
#endif

const size_t SIZE = 2000;
VV<ll> edges(SIZE);
ll N;
string S;
bitset<SIZE> bs;
const ll inf = 5e15;

PLL dfs(ll cur, ll pre) {
    ll cnt = bs.test(cur), dsum = 0;
    for (ll nxt : edges[cur]) if (nxt != pre) {
        ll a, b;
        tie(a, b) = dfs(nxt, cur);
        cnt += a;
        dsum += b;
    }
    return PLL(cnt, dsum + cnt);
}

PLL dfs_dp(ll cur, ll pre) {
    ll cnt = bs.test(cur), dsum = 0, maxv = 0;
    for (ll nxt : edges[cur]) if (nxt != pre) {
        ll a, b;
        tie(a, b) = dfs_dp(nxt, cur);
        chmax(maxv, b);
        cnt += a;
        dsum += b;
    }
    ll v = (dsum - maxv < maxv ? maxv - (dsum - maxv) : 0);
    return PLL(cnt, v + cnt);
}

bool check(ll cur, ll pre, ll sum, ll val) {
    ll dp = dfs_dp(cur, pre).second;
    ll rest = sum - val;
    return dp <= rest;
}

ll calc(ll root) {
    V<PLL> res;
    ll sum = 0;
    for (ll nxt : edges[root]) {
        auto tmp = dfs(nxt, root);
        sum += tmp.second;
        res.push_back(tmp);
    }

    DEBUG(make_tuple(root, res));
    if (sum & 1) return inf;
    for (ll i = 0; i < edges[root].size(); i++) {
        auto e = res[i];
        ll a = e.second;
        if (sum - a < a && !check(edges[root][i], root, sum, a)) return inf;
    }
    DEBUG(make_tuple(root, sum));
    return sum / 2;
}

ll solve() {
    cin >> N >> S;
    for (ll i = 1; i < N; i++) {
        ll u, v;
        cin >> u >> v;
        u--; v--;
        edges[u].push_back(v);
        edges[v].push_back(u);
    }
    for (ll i = 0; i < N; i++) if (S[i] == '1') bs.set(i, 1);
    if (bs.count() == 1) return 0;
    ll ans = inf;
    for (ll i = 0; i < N; i++) chmin(ans, calc(i));
    return ans == inf ? -1 : ans;
}

int main() {
    cout << solve() << endl;
    return 0;
}


Measured memory_bytes: 512