#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")


#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define repk(i, k, n) for (int i = k; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
#define mod3 100000007
#define vi vector<int>
#define vs vector<string>
#define vc vector<char>
#define vl vector<ll>
#define vb vector<bool>
#define vvi vector<vector<int>>
#define vvc vector<vector<char>>
#define vvl vector<vector<ll>>
#define vvb vector<vector<bool>>
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define pii pair<int,int>
#define pil pair<int,ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpii vector<pair<int,int>>
#define vpll vector<pair<ll,ll>>
#define vvpii vector<vector<pair<int,int>>>
#define vvpll vector<vector<pair<ll,ll>>>

template<typename T> void debug(T e){
    cerr << e << endl;
}

template<typename T> void debug(vector<T> &v){
    rep(i, v.size()){
        cerr << v[i] << " ";
    }
    cerr << endl;
}

template<typename T> void debug(vector<vector<T>> &v){
    rep(i, v.size()){
        rep(j, v[i].size()){
            cerr << v[i][j] << " ";
        }
        cerr << endl;
    }
}

template<typename T> void debug(vector<pair<T, T>> &v){
    rep(i,v.size()){
        cerr << v[i].first << " " << v[i].second << endl;
    }
}

template<typename T> void debug(set<T> &st){
    for (auto itr = st.begin(); itr != st.end(); itr++){
        cerr << *itr << " ";
    }
    cerr << endl;
}

template<typename T> void debug(multiset<T> &ms){
    for (auto itr = ms.begin(); itr != ms.end(); itr++){
        cerr << *itr << " ";
    }
    cerr << endl;
}

template<typename T> void debug(map<T, T> &mp){
    for (auto itr = mp.begin(); itr != mp.end(); itr++){
        cerr << itr->first << " " << itr->second << endl;
    }
}

void debug_out(){
    cerr << endl;
}

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T){
    cerr << H << " ";
    debug_out(T...);
}

void dijkstra(vvpll &graph, ll v, vl &dist, vl &cnt){
    priority_queue<pll, vpll, greater<pll>> pque;
    vector<bool> decided(graph.size());
    pque.push(pll(0, v));
    cnt[v] = 1;
    dist[v] = 0;
    while(pque.size()){
        pll p = pque.top();
        pque.pop();
        if (dist[p.second] < p.first){
            continue;
        }
        decided[p.second] = true;
        for (auto x: graph[p.second]){
            if (dist[x.first] + x.second == dist[p.second] && decided[x.first]){
                cnt[p.second] = (cnt[p.second] + cnt[x.first]) % mod1;
            }
        }
        for (auto x: graph[p.second]){
            if (dist[x.first] > dist[p.second] + x.second){
                dist[x.first] = dist[p.second] + x.second;
                pque.push(pll(dist[x.first], x.first));
            }
        }
    }
}



int main(){
    ll N, M;
    cin >> N >> M;
    vl a(M);
    vl b(M);
    rep(i,M){
        cin >> a[i] >> b[i];
        a[i]--;
        b[i]--;
    }
    vl c(N);
    rep(i,N) cin >> c[i];

    ll ans = M + 1;
    
    if (M <= 2){
        for (ll i = 0; i < (1 << M); i++){
            vl cnt(N, 0);
            rep(j, N) cnt[j] = c[j];
            ll popcnt = 0;
            for (ll j = 0; j < M; j++){
                if ((i >> j) & 1){
                    cnt[a[j]] ^= 1;
                    cnt[b[j]] ^= 1;
                    popcnt++;
                }
            }
            bool pos = true;
            rep(j, N){
                if (cnt[j] == 1) pos = false;
            }
            if (pos){
                ans = min(ans, popcnt);
            }
        }
    }
    else{
        ll c_bit = 0;
        for (ll i = 0; i < N; i++){
            if (c[i] == 1) c_bit += (1LL << i);
        }
        vpll former(0);
        vpll latter(0);
        for (ll i = 0; i < (1LL << (M / 2)); i++){
            ll pop_cnt = 0;
            vl change(N, 0);
            for (ll j = 0; j < (M / 2); j++){
                if ((i >> j) & 1){
                    pop_cnt++;
                    change[a[j]] ^= 1;
                    change[b[j]] ^= 1;
                }
            }
            ll change_bit = 0;
            for (ll j = 0; j < N; j++){
                if (change[j] == 1){
                    change_bit += (1LL << j);
                }
            }
            former.push_back(pll(pop_cnt, change_bit));
        }
        for (ll i = 0; i < (1LL << (M - M / 2)); i++){
            ll pop_cnt = 0;
            vl change(N, 0);
            for (ll j = 0; j < (M - M / 2); j++){
                if ((i >> j) & 1){
                    pop_cnt++;
                    change[a[j + M / 2]] ^= 1;
                    change[b[j + M / 2]] ^= 1;
                }
            }
            ll change_bit = 0;
            for (ll j = 0; j < N; j++){
                if (change[j] == 1){
                    change_bit += (1LL << j);
                }
            }
            latter.push_back(pll(pop_cnt, change_bit));
        }
        unordered_map<ll, ll> lattmap;
        for (ll i = 0; i < latter.size(); i++){
            if (lattmap[latter[i].second] == 0) lattmap[latter[i].second] = latter[i].first;
            else lattmap[latter[i].second] = min(lattmap[latter[i].second], latter[i].first);
        }
        //debug(c_bit);
        for (ll i = 0; i < former.size(); i++){
            //debug_out(former[i].second, former[i].first, lattmap[former[i].second ^ c_bit]);
            if ((former[i].second ^ c_bit) == 0) ans = min(ans, former[i].first);
            else{
                if (lattmap[former[i].second ^ c_bit] >= 1){
                    ans = min(ans, former[i].first + lattmap[former[i].second ^ c_bit]);
                }
            }
        }
    }
    if (ans == M + 1) cout << -1 << endl;
    else cout << ans << endl;
}