#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 998244353;
// constexpr int MOD = 1000000007;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  int n, m; cin >> n >> m;
  vector<int> a(m), b(m);
  REP(i, m) cin >> a[i] >> b[i], --a[i], --b[i];
  ll c = 0;
  REP(i, n) {
    ll c_i; cin >> c_i;
    c |= c_i << i;
  }
  map<ll, int> dp;
  REP(bit, 1 << (m / 2)) {
    ll color = c;
    REP(i, m / 2) {
      if (bit >> i & 1) {
        color ^= 1LL << a[i];
        color ^= 1LL << b[i];
      }
    }
    auto it = dp.find(color);
    if (it == dp.end()) it = dp.emplace(color, INF).first;
    chmin(it->second, popcount(static_cast<unsigned long long>(bit)));
  }
  ll ans = LINF;
  REP(bit, 1 << ((m + 1) / 2)) {
    ll color = 0;
    REP(i, (m + 1) / 2) {
      if (bit >> i & 1) {
        color ^= 1LL << a[m / 2 + i];
        color ^= 1LL << b[m / 2 + i];
      }
    }
    auto it = dp.find(color);
    if (it != dp.end()) {
      chmin(ans, it->second + popcount(static_cast<unsigned long long>(bit)));
    }
  }
  cout << (ans == LINF ? -1 : ans) << '\n';
  return 0;
}