#include <bits/stdc++.h>

using namespace std;
#define SZ(x) (int) (x).size()
#define REP(i, n) for(int i = 0; i < (n); i++)
#define FOR(i, a, b) for(auto i = (a); i < (b); i++)
#define For(i, a, b, c) \
	for(auto i = (a); i != (b); i += (c))
#define REPR(i, n) for(auto i = (n) -1; i >= 0; i--)
#define ALL(s) (s).begin(), (s).end()
#define so(V) sort(ALL(V))
#define rev(V) reverse(ALL(V))
#define uni(v) v.erase(unique(ALL(v)), (v).end())
#define eb emplace_back

typedef unsigned long long ull;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<bool> vb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> PI;
typedef pair<ll, ll> PL;
const double EPS = 1e-6;
const int MOD = 1e9 + 7;
const int INF = (1 << 30);
const ll LINF = 1e18;
const double math_PI = acos(-1);

template<typename T>
vector<T> make_v(size_t a) {
	return vector<T>(a);
}

template<typename T, typename... Ts>
auto make_v(size_t a, Ts... ts) {
	return vector<decltype(make_v<T>(ts...))>(
		a, make_v<T>(ts...));
}

template<typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill_v(
	T& t, const V& v) {
	t = v;
}

template<typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill_v(
	T& t, const V& v) {
	for(auto& e: t) fill_v(e, v);
}

template<class T>
bool chmax(T& a, const T& b) {
	if(a < b) {
		a = b;
		return true;
	}
	return false;
}

template<class T>
bool chmin(T& a, const T& b) {
	if(a > b) {
		a = b;
		return true;
	}
	return false;
}

template<typename S, typename T>
istream& operator>>(istream& is, pair<S, T>& p) {
	cin >> p.first >> p.second;
	return is;
}

template<typename T>
istream& operator>>(istream& is, vector<T>& vec) {
	for(T& x: vec) is >> x;
	return is;
}

template<typename T>
string join(vector<T>& vec, string splitter) {
	stringstream ss;
	REP(i, SZ(vec)) {
		if(i != 0) ss << splitter;
		ss << vec[i];
	}
	return ss.str();
}

template<typename T>
ostream& operator<<(ostream& os, vector<T>& vec) {
	os << join(vec, " ");
	return os;
}
template<class T = ll>
struct Edge {
public:
	int from, to;
	T cost;
	Edge() {
	}
	Edge(int _from, int _to, T _cost) {
		from = _from;
		to = _to;
		cost = _cost;
	}
};
template<class T = ll>
using Edges = vector<Edge<T>>;
template<class T = ll>
using Graph = vector<Edges<T>>;

int main() {
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	int N, M;
	cin >> N >> M;
	vll V(M);
	REP(i, M) {
		int a, b;
		cin >> a >> b;
		a--;
		b--;
		V[i] = (1ll << a) | (1ll << b);
	}
	vi C(N);
	cin >> C;
	ll goal = 0;
	REPR(i, N) {
		goal <<= 1ll;
		goal += C[i];
	}
	map<ll, int> half;
	int a = M / 2;
	int b = M - a;
	REP(bit, 1ll << a) {
		ll cur = 0;
		int cnt = 0;
		REP(i, a) {
			if(bit >> i & 1) {
				cur ^= V[i];
				cnt++;
			}
		}
		if(half.count(cur) == 0) {
			half[cur] = cnt;
		} else {
			chmin(half[cur], cnt);
		}
	}
	int ans = INF;
	REP(bit, 1ll << b) {
		ll cur = 0;
		int cnt = 0;
		REP(i, b) {
			if(bit >> i & 1) {
				cur ^= V[a + i];
				cnt++;
			}
		}
		ll target = cur ^ goal;
		if(half.count(target)) {
			chmin(ans, half[target] + cnt);
		}
	}
	if(ans == INF)
		cout << -1 << endl;
	else
		cout << ans << endl;
	return 0;
}