n,m = map(int,input().split())
a = []
b = []
for _ in range(m):
    ai, bi = map(int,input().split())
    a.append(ai-1)
    b.append(bi-1)
cv = list(map(int,input().split()))
c = 0
for i in range(n):
    if cv[i]:
        c += (1 << i)
seen = set()
val = dict()
m1 = m // 2
m2 = m - m1
for bt in range((1 << m1)):
    l = 0
    for i in range(m1):
        if (bt >> i) & 1:
            l ^= (1 << a[i])
            l ^= (1 << b[i])
    if l in seen:
        val[l] = min(val[l], bin(bt).count("1"))
    else:
        val[l] = bin(bt).count("1")
        seen.add(l)
ans = 100000000
for bt in range(1 << m2):
    l = c
    for i in range(m2):
        if (bt >> i) & 1:
            l ^= (1 << a[m1+i])
            l ^= (1 << b[m1+i])
    if l in seen:
        ans = min(ans, val[l] + bin(bt).count("1"))
if ans == 100000000:
    print(-1)
else:
    print(ans)