#include <bits/stdc++.h>
using namespace std ;
#define fast_input_output ios::sync_with_stdio(false); cin.tie(nullptr);
// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
#pragma GCC target("avx")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
typedef long long ll ;
typedef long double ld ;
typedef pair<ll,ll> P ;
typedef tuple<ll,ll,ll> TP ;
#define chmin(a,b) a = min(a,b)
#define chmax(a,b) a = max(a,b)
#define bit_count(x) __builtin_popcountll(x)
#define gcd(a,b) __gcd(a,b)
#define lcm(a,b) a / gcd(a,b) * b
#define rep(i,n) for(int i = 0 ; i < n ; i++)
#define rrep(i,a,b) for(int i = a ; i < b ; i++)
#define repi(it,S) for(auto it = S.begin() ; it != S.end() ; it++)
#define pt(a) cout << a << endl
#define DEBUG(...) ; cout << #__VA_ARGS__ << endl ; for(auto x : {__VA_ARGS__}) cout << x << "  " ; cout << endl ;
#define DEBUG_LIST(...) cout << #__VA_ARGS__ << endl ; DEBUG_REP(__VA_ARGS__) ;
#define DEBUG_REP(V) cout << "{ " ; repi(itr,V) cout << *itr << ", " ; cout << "}" << endl ;
#define debug(a) cout << #a << " " << a << endl
#define all(a) a.begin(), a.end()
#define endl "\n"

int n, m;

vector<int> A, B, C;
vector<bool> X[1<<20];
vector<bool> Y[1<<20];

int main(){
    fast_input_output
    cin >> n >> m;
    A.resize(m);
    B.resize(m);
    C.resize(n);
    rep(i,m) cin >> A[i] >> B[i], A[i]--, B[i]--;
    rep(i,n) cin >> C[i];
    vector<pair<ll,int>> vec;
    rep(S,1<<m/2){
        vector<int> U(n,0);
        rep(i,m/2){
            if(S >> i & 1) {
                U[A[i]] ^= 1;
                U[B[i]] ^= 1;
            }
        }
        ll res = 0;
        rep(i,n) {
            res *= 2;
            res += (U[i] ^ C[i]);
        }
        vec.push_back({res,bit_count(S)});
    }
    sort(all(vec));
    int ans = 1e8;
    rep(S,1<<(m-m/2)){
        vector<int> U(n,0);
        rep(i,m-m/2){
            if(S >> i & 1) {
                U[A[i+m/2]] ^= 1;
                U[B[i+m/2]] ^= 1;
            }
        }
        ll res = 0;
        rep(i,n) {
            res *= 2;
            res += U[i];
        }
        auto it = lower_bound(all(vec),pair<ll,int>(res,-1));
        if((*it).first == res) chmin(ans,(*it).second + bit_count(S));
    }
    if(ans == 1e8) ans = -1;
    cout << ans << endl;
}