#include <bits/stdc++.h>
using namespace std;
#define pb push_back
using ll = long long;
using vi = vector <int>;
const ll mod = 1e9 + 7;

const int N = 40;

int u[N], v[N];

int main() {
	ios::sync_with_stdio(0);
	
	int n, m; cin >> n >> m;
	for(int i = 0; i < m; i ++) {
		cin >> u[i] >> v[i];
		u[i] --;
		v[i] --;
	}
	
	ll goal = 0;
	for(int i = 0; i < n; i ++) {
		int x; cin >> x;
		if(x) goal |= (1LL << i);
	}
	
	int l = m / 2, r = m - l;
	
	map <ll, int> mp;
	
	for(int k = 0; k < (1 << l); k ++) {
		ll t = 0;
		int c = __builtin_popcount(k);
		for(int i = 0; i < l; i ++) if((k >> i) & 1) {
			t ^= (1LL << u[i]);
			t ^= (1LL << v[i]);
		}
		
		if(mp.find(t) != mp.end())
			mp[t] = min(mp[t], c);
		else
			mp[t] = c;
	}
	
	int ans = m + 1;
	
	for(int k = 0; k < (1 << r); k ++) {
		ll t = 0;
		int c = __builtin_popcount(k);
		for(int i = l; i < m; i ++) if((k >> (i - l)) & 1) {
			t ^= (1LL << u[i]);
			t ^= (1LL << v[i]);
		}
		
		if(mp.find(t ^ goal) != mp.end())
			ans = min(ans, mp[t ^ goal] + c);
	}
	
	if(ans == m + 1) ans = -1;
	cout << ans << '\n';
}