import sys

# sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = (1 << 63)-1
# inf = (1 << 31)-1
md = 10**9+7
# md = 998244353

from collections import defaultdict

def popcnt(a): return bin(a).count("1")

def mim(ab):
    res = defaultdict(lambda: inf)
    for s in range(1 << len(ab)):
        cur = 0
        for i, (a, b) in enumerate(ab):
            if s >> i & 1:
                cur ^= 1 << a
                cur ^= 1 << b
        res[cur] = min(res[cur], popcnt(s))
    return res

n, m = LI()
ab = LLI1(m)
c = sum(a << i for i, a in enumerate(LI()))
ll = mim(ab[:m//2])
rr = mim(ab[m//2:])

ans = inf
for l in ll:
    r = c ^ l
    if r in rr:
        ans = min(ans, ll[l]+rr[r])

if ans == inf: ans = -1
print(ans)