import sys
readline=sys.stdin.readline
from collections import defaultdict

N,M=map(int,readline().split())
A,B=[],[]
for m in range(M):
    a,b=map(int,readline().split())
    a-=1;b-=1
    A.append(a)
    B.append(b)
inf=1<<60
m=M//2
dct=defaultdict(lambda:inf)
for bit in range(1<<m):
    c=0
    for i in range(m):
        if bit&1<<i:
            c^=1<<A[i]
            c^=1<<B[i]
    dct[c]=min(dct[c],sum(1 for i in range(m) if bit&1<<i))
C=sum(c<<i for i,c in enumerate(map(int,readline().split())))
ans=inf
for bit in range(1<<M-m):
    c=0
    for i in range(M-m):
        if bit&1<<i:
            c^=1<<A[m+i]
            c^=1<<B[m+i]
    ans=min(ans,dct[C^c]+sum(1 for i in range(M-m) if bit&1<<i))
if ans==inf:
    ans=-1
print(ans)