#include <bits/stdc++.h>
using namespace std;
#define ar array
#define int long long
#define ld long double
#define crash assert(69 == 420)
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
const int MOD = 1e9 + 7;
const int INF = 1e9;
const int N = 2e5 + 20;
const int LOG = 20;
int dp[N][2][2];
bool A[N];
vector<int> g[N];
void dfs(int x,int p){
dp[x][A[x]][0] = 0;
dp[x][A[x] ^ 1][1] = 1;
for(auto u: g[x]){
if(u == p)continue;
dfs(u, x);
int ndp[2][2];
for(int i = 0;i < 2;i++){
for(int j = 0;j < 2;j++)ndp[i][j] = INF;
}
for(int i = 0;i < 2;i++){
for(int j = 0;j < 2;j++){
for(int k = 0;k < 2;k ++){
ndp[i ^ j][k] = min(ndp[i ^ j][k], dp[x][i][k] + dp[u][k][j]);
}
}
}
memcpy(dp[x], ndp, sizeof ndp);
}
}
signed main(){ios_base::sync_with_stdio(false);cin.tie(0);
int n;
cin>>n;
for(int i = 1;i < n;i++){
int u, v;
cin>>u>>v;
--u, --v;
g[u].push_back(v);
g[v].push_back(u);
}
for(int i = 0;i < n;i++)cin>>A[i];
for(int i = 0;i < n;i++){
for(int j = 0;j < 2;j++){
for(int k = 0;k < 2;k++)dp[i][j][k] = INF;
}
}
dfs(0, 0);
int ans = min(dp[0][0][0], dp[0][0][1]);
if(ans >= INF)ans = -1;
cout<<ans;
}
