#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint1000000007;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001
int n,m;
void go(vector<pair<int,int>> a,map<long long,int> &mp){
	int mm = a.size();
	rep(i,1<<mm){
		long long B = 0;
		int s = 0;
		rep(j,mm){
			if((i>>j)&1){
				B ^= 1LL<<a[j].first;
				B ^= 1LL<<a[j].second;
				s++;
			}
		}
		if(mp.count(B))mp[B] = min(mp[B],s);
		else mp[B] = s;
	}
}
		

int main(){
	
	
	cin>>n>>m;
	
	vector<pair<int,int>> a,b;
	rep(i,m){
		int x,y;
		cin>>x>>y;
		x--,y--;
		if(a.size()<20){
			a.emplace_back(x,y);
		}
		else{
			b.emplace_back(x,y);
		}
	}
	
	map<long long,int> mp1,mp2;
	go(a,mp1);
	go(b,mp2);
	long long c = 0;
	rep(i,n){
		int t;
		cin>>t;
		if(t)c |= 1LL<<i;
	}
	
	int ans = Inf32;
	
	for(auto x:mp1){
		if(mp2.count(c^x.first)){
			ans = min(ans,x.second + mp2[c^x.first]);
		}
	}
	
	
	if(ans==Inf32)ans = -1;
	cout<<ans<<endl;
	
	return 0;
}