N,M = map(int,input().split())
edge = []
for _ in range(M):
    a,b = map(int,input().split())
    a -= 1
    b -= 1
    edge.append((1 << a) | (1 << b))
c = list(map(int,input().split()))
C = 0
for i in range(N):
    if c[i] == 1:
        C |= 1 << i
import sys
D = M // 2
E = M - D
d = dict()
for bit in range(1 << D):
    count = 0
    tmp = 0
    for i in range(D):
        if bit >> i & 1:
            count += 1
            tmp ^= edge[i]
    if tmp in d:
        d[tmp] = min(d[tmp],count)
    else:
        d[tmp] = count
ans = 50
for bit in range(1 << E):
    count = 0
    tmp = 0
    for i in range(E):
        if bit >> i & 1:
            count += 1
            tmp ^= edge[D + i]
    if tmp ^ C in d:
        ans = min(ans,count + d[tmp ^ C])
if ans == 50:
    print(-1)
else:
    print(ans)