#include using namespace atcoder; #include using namespace std; // #include #pragma GCC target("avx2") #pragma GCC optimize("O3") #pragma GCC optimize("unroll-loops") #define rep(i, n) for (int i = 0; i < (int)(n); i++) #define rep2(i,a,b) for (int i = (int)(a); i < (int)(b); i++) #define all(v) v.begin(),v.end() #define inc(x,l,r) ((l)<=(x)&&(x)<(r)) #define Unique(x) sort(all(x)), x.erase(unique(all(x)), x.end()) #define pcnt __builtin_popcountll typedef long long ll; #define int ll using ld = long double; using vi = vector; using vs = vector; using P = pair; using vp = vector

; // using Bint = boost::multiprecision::cpp_int; template bool chmax(T1 &a, const T2 b) {if (a < b) {a = b; return true;} else return false; } template bool chmin(T1 &a, const T2 b) {if (a > b) {a = b; return true;} else return false; } template using priority_queue_greater = priority_queue, greater>; template ostream &operator<<(ostream &os,const vector &v){rep(i,v.size())os< istream &operator>>(istream& is,vector &v){for(T &in:v)is>>in;return is;} template ostream &operator<< (ostream &os, const pair &p){os << p.first <<" "<> (istream &is, modint1000000007 &m){ll in;is>>in;m=in;return is;} ostream &operator<< (ostream &os, const modint998244353 &m){os << m.val();return os;} istream &operator>> (istream &is, modint998244353 &m){ll in;is>>in;m=in;return is;} template void input(T&... a){(cin>> ... >> a);} template void print(T& a){cout < void print(const T&a, const Ts&... b){cout<< a;(cout<<...<<(cout<<' ',b));cout<<'\n';} #define VI(v,n) vi v(n); input(v) #define INT(...) int __VA_ARGS__; input(__VA_ARGS__) #define STR(...) string __VA_ARGS__; input(__VA_ARGS__) #define CHAR(...) char __VA_ARGS__; input(__VA_ARGS__) int sign(int x){return x>0?1:x<0?-1:0;} int ceil(int x,int y){assert(y!=0);if(sign(x)==sign(y))return (x+y-1)/y;return -((-x/y));} int floor(int x,int y){assert(y!=0);if(sign(x)==sign(y))return x/y;if(y<0)x*=-1,y*=-1;return x/y-(x%y<0);} int abs(int x,int y){return abs(x-y);} bool ins(string s,string t){return s.find(t)!=string::npos;} P operator+ (const P &p, const P &q){ return P{p.first+q.first,p.second+q.second};} P operator- (const P &p, const P &q){ return P{p.first-q.first,p.second-q.second};} void yesno(bool ok,string y="Yes",string n="No"){ cout<<(ok?y:n)< G(n); rep(i,n-1){ INT(a,b); --a;--b; G[a].push_back(b); G[b].push_back(a); } vi c(n);cin>>c; int ans = 0; auto dfs = [&](auto f,int cu,int pa) -> void { for(auto v:G[cu]){ if(v==pa)continue; f(f,v,cu); if(c[v]==0){ c[v]^=1; c[cu]^=1; ans++; } } }; dfs(dfs,0,-1); if(c[0]==0)ans=-1; print(ans); return 0; }