#include<bits/stdc++.h>
using namespace std;
const int N=44;
int n,m;
int a[N],b[N],x;
long long s;
map<long long,int>mp;
int main(){
	scanf("%d%d",&n,&m);
	for (int i=1;i<=m;i++) scanf("%d%d",&a[i],&b[i]);
	for (int i=1;i<=n;i++){
		scanf("%d",&x);
		if (x) s+=(1ll<<(i-1));
	}
	int w=(m/2);
	for (int i=0;i<(1<<w);i++){
		long long t=0;
		int sum=0;
		for (int j=0;j<w;j++) if ((i>>j)&1) t^=(1ll<<(a[j+1]-1))^(1ll<<(b[j+1]-1)),sum++;
		if (!mp[s^t]) mp[s^t]=sum+1;
		else mp[s^t]=min(mp[s^t],sum+1);
	}
	int ans=m+1;
	for (int i=0;i<(1<<(m-w));i++){
		long long t=0;
		int sum=0;
		for (int j=0;j<(m-w);j++) if ((i>>j)&1) t^=(1ll<<(a[j+1+w]-1))^(1ll<<(b[j+1+w]-1)),sum++;
		if (mp[t]) ans=min(ans,mp[t]+sum-1);
 	}
	if (ans==(m+1)) puts("-1"); else printf("%d\n",ans);
}