#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, u, v;
    cin >> n;
    vector<vector<int>> g(n);
    vector<int> c(n), wv;
    for(int i = 1; i < n; i++){
        cin >> u >> v;
        g[--u].push_back(--v);
        g[v].push_back(u);
    }
    for(int i = 0; i < n; i++){
        cin >> c[i];
        if(c[i] == 0)wv.push_back(i);
    }
    if(wv.size() & 1){
        cout << -1 << '\n';
        return 0;
    }
    vector<vector<int>> dp(n, vector<int>(2, 1 << 29));
    function<void(int,int)> dfs = [&](int v, int p){
        vector<int>& temp = dp[v];
        temp[c[v] ^ 1] = 0;
        for(auto &&u:g[v]){
            if(u == p)continue;
            dfs(u, v);
            vector<int> nxt(2, 1 << 30);
            for(int i = 0; i < 2; i++){
                for(int j = 0; j < 2; j++){
                    nxt[i ^ j] = min(nxt[i ^ j], temp[i] + dp[u][j] + j);
                }
            }
            swap(temp, nxt);
        }
    };
    dfs(0, -1);
    cout << dp[0][0] << '\n';
}