#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define ALL(x) (x).begin(), (x).end()
#ifdef LOCAL
#include "debug.hpp"
#else
#define debug(...) void(0)
#endif

template <typename T> istream& operator>>(istream& is, vector<T>& v) {
    for (T& x : v) is >> x;
    return is;
}
template <typename T> ostream& operator<<(ostream& os, const vector<T>& v) {
    for (size_t i = 0; i < v.size(); i++) {
        os << v[i] << (i + 1 == v.size() ? "" : " ");
    }
    return os;
}

template <typename T> T gcd(T x, T y) { return y != 0 ? gcd(y, x % y) : x; }
template <typename T> T lcm(T x, T y) { return x / gcd(x, y) * y; }

int topbit(signed t) { return t == 0 ? -1 : 31 - __builtin_clz(t); }
int topbit(long long t) { return t == 0 ? -1 : 63 - __builtin_clzll(t); }
int botbit(signed a) { return a == 0 ? 32 : __builtin_ctz(a); }
int botbit(long long a) { return a == 0 ? 64 : __builtin_ctzll(a); }
int popcount(signed t) { return __builtin_popcount(t); }
int popcount(long long t) { return __builtin_popcountll(t); }
bool ispow2(int i) { return i && (i & -i) == i; }
long long MSK(int n) { return (1LL << n) - 1; }

template <class T> T ceil(T x, T y) {
    assert(y >= 1);
    return (x > 0 ? (x + y - 1) / y : x / y);
}
template <class T> T floor(T x, T y) {
    assert(y >= 1);
    return (x > 0 ? x / y : (x - y + 1) / y);
}

template <class T1, class T2> inline bool chmin(T1& a, T2 b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template <class T1, class T2> inline bool chmax(T1& a, T2 b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

template <typename T> void mkuni(vector<T>& v) {
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
}
template <typename T> int lwb(const vector<T>& v, const T& x) { return lower_bound(v.begin(), v.end(), x) - v.begin(); }

const int INF = (1 << 30) - 1;
const long long IINF = (1LL << 60) - 1;
const int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
const int MOD = 998244353;
// const int MOD = 1000000007;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N, M;
    cin >> N >> M;
    vector<int> a(M), b(M);
    for (int i = 0; i < M; i++) cin >> a[i] >> b[i], a[i]--, b[i]--;
    ll c = 0;
    for (int i = 0; i < N; i++) {
        ll x;
        cin >> x;
        c |= x << i;
    }

    vector<map<ll, int>> dp(2);
    dp[0][c] = 0;
    dp[1][0] = 0;
    for (int k = 0; k < M; k++) {
        map<ll, int> ndp;
        for (auto [mask, val] : dp[0]) {
            if (not ndp.count(mask))
                ndp[mask] = val;
            else
                ndp[mask] = min(ndp[mask], val);
            int nmask = mask ^ (1LL << a[k]) ^ (1LL << b[k]);
            if (not ndp.count(nmask))
                ndp[nmask] = val + 1;
            else
                ndp[nmask] = min(ndp[nmask], val + 1);
        }
        swap(dp[0], ndp);
        swap(dp[0], dp[1]);
    }

    int ans = INF;
    for (auto [mask, val] : dp[0]) {
        if (not dp[1].count(mask)) continue;
        ans = min(ans, val + dp[1][mask]);
    }
    cout << (ans == INF ? -1 : ans) << '\n';
    return 0;
}