#include<iostream>
#include<vector>
#include<algorithm>
#include<cstring>
#include<cassert>
#include<cmath>
#include<ctime>
#include<iomanip>
#include<numeric>
#include<stack>
#include<queue>
#include<map>
#include<unordered_map>
#include<set>
#include<unordered_set>
#include<bitset>
#include<random>
using namespace std;
int N,C[2 << 17],W[2 << 17];
vector<int> G[2 << 17];
long long dp[2 << 17];
void dfs(int u,int p)
{
	if(C[u]) W[u] = 1;
	for(int v:G[u])if(v != p)
	{
		dfs(v,u);
		dp[u] += dp[v];
		if(W[v]%2 == 1) dp[u]++;
		W[u] += W[v];
	}
}
void solve()
{
	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 >> C[i],C[i] ^= 1;
	dfs(0,-1);
	if(W[0]%2 == 1) cout << -1 << endl;
	else cout << dp[0] << endl;
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int tt = 1;
	//cin >> tt;
	while(tt--) solve();
}