from collections import defaultdict

n,m = map(int,input().split())
a = [0] * m
b = [0] * m
for i in range(m):
	a[i], b[i] = map(int,input().split())
	a[i] -= 1
	b[i] -= 1

c = list(map(int,input().split()))
q = 0
for i in range(n):
	q ^= c[i] << i

r = m - m//2
v = defaultdict(lambda: 10 ** 9)

for i in range(1 << r):
	cnt = 0
	h = 0
	for j in range(r):
		if (i >> j & 1):
			cnt += 1
			h ^= 1 << a[m // 2 + j]
			h ^= 1 << b[m // 2 + j]
	v[h] = min(v[h], cnt)

r2 = m//2
ans = 10 ** 9

for i in range(1 << r2):
	cnt = 0
	h = 0
	for j in range(r2):
		if (i >> j & 1):
			cnt += 1
			h ^= 1 << a[j]
			h ^= 1 << b[j]
	ans = min(ans, v[q ^ h] + cnt)

if ans >= 10 ** 7:
	print(-1)
else:
	print(ans)