#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<numeric>
#include<cmath>
#include<utility>
#include<tuple>
#include<cstdint>
#include<cstdio>
#include<iomanip>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<deque>
#include<unordered_map>
#include<unordered_set>
#include<bitset>
#include<cctype>
#include<chrono>
#include<random>
#include<cassert>
#include<cstddef>
#include<iterator>
#include<string_view>
#include<type_traits>

#ifdef LOCAL
#  include "debug_print.hpp"
#  define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define debug(...) (static_cast<void>(0))
#endif

using namespace std;
#define rep(i,n) for(int i=0; i<(n); i++)
#define rrep(i,n) for(int i=(n)-1; i>=0; i--)
#define FOR(i,a,b) for(int i=(a); i<(b); i++)
#define RFOR(i,a,b) for(int i=(b-1); i>=(a); i--)
#define ALL(v) v.begin(), v.end()
#define RALL(v) v.rbegin(), v.rend()
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
#define pb push_back
using ll = long long;
using D = double;
using LD = long double;
using P = pair<int, int>;
template<typename T> using PQ = priority_queue<T,vector<T>>;
template<typename T> using minPQ = priority_queue<T, vector<T>, greater<T>>;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
void yesno(bool flag) {cout << (flag?"Yes":"No") << "\n";}

template<typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
    os << p.first << " " << p.second;
    return os;
}
template<typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &p) {
    is >> p.first >> p.second;
    return is;
}

template<typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
    int s = (int)v.size();
    for (int i = 0; i < s; i++) os << (i ? " " : "") << v[i];
    return os;
}
template<typename T>
istream &operator>>(istream &is, vector<T> &v) {
    for (auto &x : v) is >> x;
    return is;
}
void in() {}
template<typename T, class... U>
void in(T &t, U &...u) {
    cin >> t;
    in(u...);
}
void out() { cout << "\n"; }
template<typename T, class... U, char sep = ' '>
void out(const T &t, const U &...u) {
    cout << t;
    if (sizeof...(u)) cout << sep;
    out(u...);
}
void outr() {}
template<typename T, class... U, char sep = ' '>
void outr(const T &t, const U &...u) {
    cout << t;
    outr(u...);
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int n,m; in(n,m);
    vector<vector<P>> g(n);
    vector<int> a,b;
    rep(i,m){
        int x,y; in(x,y); x--; y--;
        g[x].pb({y,i});
        g[y].pb({x,i});
        a.pb(x);
        b.pb(y);
    }
    vector<int> c(n); in(c);
    vector<vector<int>> ed(n),vs(n);
    vector<bool> seen_v(n,false);
    vector<bool> seen_e(m,false);
    int now = 0;
    rep(i,n){
        if(seen_v[i]) continue;
        seen_v[i] = true;
        queue<int> q;
        q.push({i});
        vs[now].pb(i);
        while(q.size()){
            int x = q.front(); q.pop();
            for (auto [y,idx] : g[x]){
                if(!seen_e[idx]) {
                    seen_e[idx] = true;
                    ed[now].pb(idx);
                }
                if(!seen_v[y]){
                    seen_v[y] = true;
                    vs[now].pb(y);
                    q.push(y);
                }
            }
        }
        now++;
    }
    const int inf = 1e9;
    int ans = 0;
    rep(i,now){
        auto &v = ed[i];
        int k = v.size();
        int h = k/2;
        int l = k-h;
        vector<ll> msk1(1 << h), msk2(1 << l);
        rep(bit, (1 << h)){
            rep(j,h){
                if((bit >> j) & 1){
                    msk1[bit] ^= (1LL << a[v[j]]);
                    msk1[bit] ^= (1LL << b[v[j]]);
                }
            }
        }
        rep(bit, (1 << l)){
            rep(j,l){
                if((bit >> j) & 1){
                    msk2[bit] ^= (1LL << a[v[j+h]]);
                    msk2[bit] ^= (1LL << b[v[j+h]]);
                }
            }
        }
        ll state = 0;
        for(int ent : vs[i]){
            if(c[ent]) state |= (1LL << ent);
        }
        map<ll,int> mp;
        rep(bit, (1 << l)){
            if(!mp.count(msk2[bit])) mp[msk2[bit]] = __builtin_popcountll(bit);
            else chmin(mp[msk2[bit]], __builtin_popcountll(bit));
        }
        int tmp = inf;
        rep(bit, (1 << h)){
            ll rem = state ^ msk1[bit];
            if(!mp.count(rem)) continue;
            chmin(tmp, mp[rem] + __builtin_popcountll(msk1[bit]));
        }
        if(tmp == inf){
            out(-1);
            return 0;
        }
        ans += tmp;
    }
    out(ans);
}