#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")


#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define repk(i, k, n) for (int i = k; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
#define mod3 100000007
#define vi vector<int>
#define vs vector<string>
#define vc vector<char>
#define vl vector<ll>
#define vb vector<bool>
#define vvi vector<vector<int>>
#define vvc vector<vector<char>>
#define vvl vector<vector<ll>>
#define vvb vector<vector<bool>>
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define pii pair<int,int>
#define pil pair<int,ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpii vector<pair<int,int>>
#define vpll vector<pair<ll,ll>>
#define vvpii vector<vector<pair<int,int>>>
#define vvpll vector<vector<pair<ll,ll>>>

template<typename T> void debug(T e){
    cerr << e << endl;
}

template<typename T> void debug(vector<T> &v){
    rep(i, v.size()){
        cerr << v[i] << " ";
    }
    cerr << endl;
}

template<typename T> void debug(vector<vector<T>> &v){
    rep(i, v.size()){
        rep(j, v[i].size()){
            cerr << v[i][j] << " ";
        }
        cerr << endl;
    }
}

template<typename T> void debug(vector<pair<T, T>> &v){
    rep(i,v.size()){
        cerr << v[i].first << " " << v[i].second << endl;
    }
}

template<typename T> void debug(set<T> &st){
    for (auto itr = st.begin(); itr != st.end(); itr++){
        cerr << *itr << " ";
    }
    cerr << endl;
}

template<typename T> void debug(multiset<T> &ms){
    for (auto itr = ms.begin(); itr != ms.end(); itr++){
        cerr << *itr << " ";
    }
    cerr << endl;
}

template<typename T> void debug(map<T, T> &mp){
    for (auto itr = mp.begin(); itr != mp.end(); itr++){
        cerr << itr->first << " " << itr->second << endl;
    }
}

void debug_out(){
    cerr << endl;
}

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T){
    cerr << H << " ";
    debug_out(T...);
}

ll INF = 1000000;

void treedp(vvl &graph, vb &isvisited, vl &dp1, vl &dp2, vl &c, ll v){
    isvisited[v] = true;
    ll now_state = c[v];
    ll count = 0;
    for (ll x: graph[v]){
        if (isvisited[x]){
            continue;
        }
        treedp(graph, isvisited, dp1, dp2, c, x);
        ll next_state;
        if (dp1[x] == INF) next_state = 1;
        else next_state = 0;
        if (next_state == 0){
            now_state ^= 1;
            count += 1;
            count += dp1[x];
        }
        else{
            count += dp2[x];
        }
    }
    if (now_state == 0) dp1[v] = count;
    else dp2[v] = count;
}

int main(){
    ll N;
    cin >> N;
    vl a(N - 1);
    vl b(N - 1);
    vl c(N);
    rep(i,N - 1){
        cin >> a[i] >> b[i];
        a[i]--;
        b[i]--;
    }
    vvl graph(N, vl(0));
    rep(i,N  - 1){
        graph[a[i]].push_back(b[i]);
        graph[b[i]].push_back(a[i]);
    }
    rep(i,N) cin >> c[i];
    vl dp1(N, INF); //その頂点が白で塗られるとき
    vl dp2(N, INF); //その頂点が黒で塗られるとき

    vector<bool> isvisited(N, false);
    treedp(graph, isvisited, dp1, dp2, c, 0);
    //debug(dp1);
    //debug(dp2);
    if (dp2[0] == INF) cout << -1 << endl;
    else cout << dp2[0] << endl;
}