#include <bits/stdc++.h>
#define MAXN 40
#define MAXM 40
using namespace std;

int n, m, ans, A[MAXM][2];

int main() {
    scanf("%d%d", &n, &m);
    for (int i = 0; i < m; i++) {
        scanf("%d%d", &A[i][0], &A[i][1]);
        A[i][0]--; A[i][1]--;
    }
    long long goal = 0;
    for (int i = 0; i < n; i++) {
        long long x; scanf("%lld", &x);
        goal |= x << i;
    }

    unordered_map<long long, int> mp;
    int half = m / 2;
    for (int i = 0; i < (1 << half); i++) {
        long long msk = 0;
        int cnt = 0;
        for (int j = 0; j < half; j++) if (i >> j & 1) {
            msk ^= 1LL << A[j][0];
            msk ^= 1LL << A[j][1];
            cnt++;
        }
        if (mp.count(msk) == 0) mp[msk] = cnt;
        else mp[msk] = min(mp[msk], cnt);
    }

    ans = m + 1;
    for (int i = 0; i < (1 << (m - half)); i++) {
        long long msk = 0;
        int cnt = 0;
        for (int j = 0; j < m - half; j++) if (i >> j & 1) {
            msk ^= 1LL << A[j + half][0];
            msk ^= 1LL << A[j + half][1];
            cnt++;
        }
        if (mp.count(goal ^ msk)) ans = min(ans, cnt + mp[goal ^ msk]);
    }

    if (ans == m + 1) printf("-1\n");
    else printf("%d\n", ans);
    return 0;
}