def solve():
    N,M=map(int,input().split())
    a=[0]*M; b=[0]*M

    for j in range(M):
        a[j],b[j]=map(int,input().split())
        a[j]-=1; b[j]-=1

    c=list(map(int,input().split()))

    def bit(x,k):
        return (x>>k)&1

    inf=10**9
    def calc(F):
        X={}
        M=len(F)

        for S in range(1<<M):
            p=0
            cnt=0
            for k in range(M):
                if bit(S,k):
                    p^=(1<<a[F[k]])^(1<<b[F[k]])
                    cnt+=1
            if cnt<X.get(p,inf):
                X[p]=cnt
        return X

    P=calc(list(range(M//2)))
    Q=calc(list(range(M//2,M)))

    target=sum([1<<v for v in range(N) if c[v]==1])
    ans=min(P[p]+Q.get(p^target,inf) for p in P)
    return ans if ans<inf else -1

#==================================================
print(solve())