#include <bits/stdc++.h>
using namespace std;
void Init()
{
ios::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
}
typedef long long ll;
const int MAXN = 200000 + 5;
const ll INF = (ll)9e18;
int n;
vector<int> g[MAXN];
int initState[MAXN]; // 0 = off, 1 = on
ll dp[MAXN][2][2]; // dp[v][parentPress][pressV]
int parentArr[MAXN];
void Input()
{
cin >> n;
for (int i = 1; i <= n; ++i) {
g[i].clear();
initState[i] = 0;
}
for (int i = 0; i < n - 1; ++i) {
int u, v;
cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
// read states: either a single string "0101..." or n integers
string token;
cin >> token;
if ((int)token.size() == n) {
for (int i = 1; i <= n; ++i) initState[i] = token[i-1] - '0';
} else {
// token is first number
initState[1] = stoi(token);
for (int i = 2; i <= n; ++i) cin >> initState[i];
}
}
void dfs(int v, int p)
{
parentArr[v] = p;
for (int to : g[v]) if (to != p) dfs(to, v);
// for pressV = 0 and pressV = 1 compute tmp_even/tmp_odd
for (int parentPress = 0; parentPress <= 1; ++parentPress) {
for (int pressV = 0; pressV <= 1; ++pressV) {
// compute tmp for this pressV:
ll even = 0;
ll odd = INF;
for (int to : g[v]) {
if (to == p) continue;
ll cand_even = min(
(even >= INF ? INF : even + dp[to][pressV][0]),
(odd >= INF ? INF : odd + dp[to][pressV][1])
);
ll cand_odd = min(
(odd >= INF ? INF : odd + dp[to][pressV][0]),
(even >= INF ? INF : even + dp[to][pressV][1])
);
even = cand_even;
odd = cand_odd;
}
int toggles = (parentPress + pressV) & 1; // parity ignoring children
int needParity = initState[v] ^ toggles; // children parity required: s ^ parentPress ^ pressV
if (needParity == 0) {
dp[v][parentPress][pressV] = (pressV ? 1LL : 0LL) + even;
} else {
dp[v][parentPress][pressV] = (pressV ? 1LL : 0LL) + odd;
}
if (dp[v][parentPress][pressV] > INF) dp[v][parentPress][pressV] = INF;
}
}
}
void Bai()
{
// choose root = 1
dfs(1, 0);
ll ans = min(dp[1][0][0], dp[1][0][1]);
if (ans >= INF/2) cout << -1 << '\n';
else cout << ans << '\n';
}
int main()
{
Init();
Input();
Bai();
return 0;
}
