#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)4e18;
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);
}
string token;
cin >> token;
if ((int)token.size() == n) {
for (int i = 1; i <= n; ++i) initState[i] = token[i-1] - '0';
} else {
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);
// initialize dp[v] with INF
for (int i = 0; i <= 1; ++i)
for (int j = 0; j <= 1; ++j)
dp[v][i][j] = INF;
// tmp[first][second] as in editorial:
// first = whether v is pressed (0/1)
// second = parity of number of children pressed (0 = even, 1 = odd)
ll tmp[2][2];
tmp[0][0] = 0; tmp[0][1] = INF;
tmp[1][0] = 0; tmp[1][1] = INF;
for (int to : g[v]) {
if (to == p) continue;
ll newTmp[2][2];
newTmp[0][0] = newTmp[0][1] = newTmp[1][0] = newTmp[1][1] = INF;
// apply editorial merge formulas exactly
// newTmp[0][0] = min(tmp[1][0] + dp[to][0][1], tmp[0][0] + dp[to][0][0])
if (tmp[1][0] < INF && dp[to][0][1] < INF) newTmp[0][0] = min(newTmp[0][0], tmp[1][0] + dp[to][0][1]);
if (tmp[0][0] < INF && dp[to][0][0] < INF) newTmp[0][0] = min(newTmp[0][0], tmp[0][0] + dp[to][0][0]);
// newTmp[0][1] = min(tmp[1][1] + dp[to][1][1], tmp[0][1] + dp[to][1][0])
if (tmp[1][1] < INF && dp[to][1][1] < INF) newTmp[0][1] = min(newTmp[0][1], tmp[1][1] + dp[to][1][1]);
if (tmp[0][1] < INF && dp[to][1][0] < INF) newTmp[0][1] = min(newTmp[0][1], tmp[0][1] + dp[to][1][0]);
// newTmp[1][0] = min(tmp[0][0] + dp[to][0][1], tmp[1][0] + dp[to][0][0])
if (tmp[0][0] < INF && dp[to][0][1] < INF) newTmp[1][0] = min(newTmp[1][0], tmp[0][0] + dp[to][0][1]);
if (tmp[1][0] < INF && dp[to][0][0] < INF) newTmp[1][0] = min(newTmp[1][0], tmp[1][0] + dp[to][0][0]);
// newTmp[1][1] = min(tmp[0][1] + dp[to][1][1], tmp[1][1] + dp[to][1][0])
if (tmp[0][1] < INF && dp[to][1][1] < INF) newTmp[1][1] = min(newTmp[1][1], tmp[0][1] + dp[to][1][1]);
if (tmp[1][1] < INF && dp[to][1][0] < INF) newTmp[1][1] = min(newTmp[1][1], tmp[1][1] + dp[to][1][0]);
// move newTmp -> tmp
tmp[0][0] = newTmp[0][0];
tmp[0][1] = newTmp[0][1];
tmp[1][0] = newTmp[1][0];
tmp[1][1] = newTmp[1][1];
}
// now compute dp[v][i][j] for all i (parentPress) and j (pressV)
for (int i = 0; i <= 1; ++i) {
for (int j = 0; j <= 1; ++j) {
int toggles = (i + j) & 1;
// after toggles parentPress+pressV, v's state = initState[v] ^ toggles
// if that equals 1 (ON) -> need odd number of children pressed -> use tmp[j][1]
// else need even -> use tmp[j][0]
if ((initState[v] ^ toggles) == 1) {
if (tmp[j][1] < INF) dp[v][i][j] = (ll)j + tmp[j][1];
} else {
if (tmp[j][0] < INF) dp[v][i][j] = (ll)j + tmp[j][0];
}
if (dp[v][i][j] > INF) dp[v][i][j] = INF;
}
}
}
void Bai()
{
// choose root = 1 (any root works)
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;
}
