from collections import defaultdict

INF = 1<<60

N, M = map(int, input().split())
edge = [list(map(int, input().split())) for _ in range(M)]
C = list(map(int, input().split()))

dbit = 0
for i, c in enumerate(C):
    dbit ^= c<<i

L, R = edge[:M//2], edge[M//2:]
D = defaultdict(lambda : INF)
for bit in range(1<<len(L)):
    mask = dbit
    cnt = 0
    for i, (u, v) in enumerate(L):
        if 1<<i & bit:
            u, v = u-1, v-1
            mask ^= 1<<u
            mask ^= 1<<v
            cnt += 1
    D[mask] = min(D[mask], cnt)

ans = INF
for bit in range(1<<len(R)):
    mask = 0
    cnt = 0
    for i, (u, v) in enumerate(R):
        if 1<<i & bit:
            u, v = u-1, v-1
            mask ^= 1<<u
            mask ^= 1<<v
            cnt += 1
    ans = min(ans, D[mask]+cnt)

print(ans if ans != INF else -1)