MSK1 = 0x55555555555555555555555555555555
MSK2 = 0x33333333333333333333333333333333
MSK3 = 0x0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f
MSK4 = 0x00ff00ff00ff00ff00ff00ff00ff00ff
MSK5 = 0x0000ffff0000ffff0000ffff0000ffff
MSK6 = 0x00000000ffffffff00000000ffffffff
MSK7 = 0x0000000000000000ffffffffffffffff

def popcnt(x):
  x=(x & MSK1) + ((x>>1) & MSK1)
  x=(x & MSK2) + ((x>>2) & MSK2)
  x=(x & MSK3) + ((x>>4) & MSK3)
  x=(x & MSK4) + ((x>>8) & MSK4)
  x=(x & MSK5) + ((x>>16) & MSK5)
  x=(x & MSK6) + ((x>>32) & MSK6)
  x=(x & MSK7) + ((x>>64) & MSK7)
  return x

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], popcnt(bt))
    else:
        val[l] = popcnt(bt)
        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] + popcnt(bt))
if ans == 100000000:
    print(-1)
else:
    print(ans)