from collections import defaultdict

def popcount(n):
	c=(n&0x5555555555555555)+((n>>1)&0x5555555555555555)
	c=(c&0x3333333333333333)+((c>>2)&0x3333333333333333)
	c=(c&0x0f0f0f0f0f0f0f0f)+((c>>4)&0x0f0f0f0f0f0f0f0f)
	c=(c&0x00ff00ff00ff00ff)+((c>>8)&0x00ff00ff00ff00ff)
	c=(c&0x0000ffff0000ffff)+((c>>16)&0x0000ffff0000ffff)
	c=(c&0x00000000ffffffff)+((c>>32)&0x00000000ffffffff)
	return c


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()))
v = 0
for i in range(n):
	v ^= c[i] << i

r = defaultdict(lambda: 10 ** 9)
r[v] = 0

for i in range(m):
	for w, c in list(r.items()):
		x = w ^ (1 << a[i]) ^ (1 << b[i])
		if popcount(w) < popcount(x): continue
		if r[x] > c + 1:
			r[x] = c + 1

if r[0] == 10 ** 9:
	print(-1)
else:
	print(r[0])