#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, m, m1, m2, u, v;
    cin >> n >> m;
    m1 = m / 2, m2 = m - m1;
    ll S;
    vector<ll> edge1(m1), edge2(m2);
    vector<pair<ll,int>> b(1 << m2);
    for(int i = 0; i < m; i++){
        cin >> u >> v;
        u--, v--;
        if(i < m1) edge1[i] = (1ll << u) | (1ll << v);
        else edge2[i - m1] = (1ll << u) | (1ll << v);
    }
    S = 0;
    for(int i = 0; i < n; i++){
        cin >> v;
        if(v) S |= 1ll << i;
    }
    for(int i = 0; i < (1 << m2); i++){
        ll S = 0;
        for(int j = 0; j < m2; j++){
            if(i >> j & 1) S ^= edge2[j];
        }
        b[i] = make_pair(S, __builtin_popcount(i));
    }
    sort(b.begin(), b.end());
    auto f = [&](ll S){
        int j = lower_bound(b.begin(), b.end(), make_pair(S, -1)) - b.begin();
        if(j == b.size() || S != b[j].first) return 1 << 30;
        return b[j].second;
    };
    int ans = 1 << 30;
    for(int i = 0; i < (1 << m1); i++){
        ll T = 0;
        for(int j = 0; j < m1; j++){
            if(i >> j & 1) T ^= edge1[j];
        }
        ans = min(ans, f(S ^ T) + __builtin_popcount(i));
    }
    if(ans >> 30) ans = -1;
    cout << ans << '\n';
}