N, M = map(int, input().split())
edge0, edge1 = [], []
for i in range(M):
    a, b = map(int, input().split())
    if i % 2 == 0:
        edge0.append((a - 1, b - 1))
    else:
        edge1.append((a - 1, b - 1))

C = list(map(int, input().split()))
C.reverse()
goal = 0
for i in range(N):
    goal <<= 1
    goal |= C[i]

dic0 = dict()
for bit in range(1 << len(edge0)):
    state = 0
    cnt = 0
    for i in range(len(edge0)):
        if (bit >> i) & 1:
            cnt += 1
            state ^= (1 << edge0[i][0])
            state ^= (1 << edge0[i][1])
    if state not in dic0:
        dic0[state] = M
    if cnt < dic0[state]:
        dic0[state] = cnt

dic1 = dict()
for bit in range(1 << len(edge1)):
    state = 0
    cnt = 0
    for i in range(len(edge1)):
        if (bit >> i) & 1:
            cnt += 1
            state ^= (1 << edge1[i][0])
            state ^= (1 << edge1[i][1])
    if state not in dic1:
        dic1[state] = M
    if cnt < dic1[state]:
        dic1[state] = cnt

ans = M + 1
for i in dic0:
    if goal ^ i in dic1:
        if ans > dic1[goal ^ i] + dic0[i]:
            ans = dic1[goal ^ i] + dic0[i]

if ans == M + 1:
    print(-1)
else:
    print(ans)