#include <bits/stdc++.h>
#include <atcoder/all>

using namespace std;
using namespace atcoder;

#define overload4(_1, _2, _3, _4, name, ...) name
#define rep1(n) for(int i = 0; i < (int)(n); ++i)
#define rep2(i, n) for(int i = 0; i < (int)(n); ++i)
#define rep3(i, a, b) for(int i = (a); i < (int)(b); ++i)
#define rep4(i, a, b, c) for(int i = (a); i < (int)(b); i += (c))
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)

#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; --i)
#define ALL(a) a.begin(), a.end()
#define Sort(a) sort(a.begin(), a.end())
#define RSort(a) sort(a.rbegin(), a.rend())

typedef long long int ll;
typedef unsigned long long ul;
typedef long double ld;
typedef vector<int> vi;
typedef vector<long long> vll;
typedef vector<char> vc;
typedef vector<string> vst;
typedef vector<double> vd;
typedef vector<long double> vld;
typedef pair<long long, long long> P;

template<class T> long long sum(const T& a){ return accumulate(a.begin(), a.end(), 0LL); }
template<class T> auto min(const T& a){ return *min_element(a.begin(), a.end()); }
template<class T> auto max(const T& a){ return *max_element(a.begin(), a.end()); }
template<class T> bool insec(const T& a, const T& l, const T& r){ return l <= a && a < r; }

const long long MINF = 0x7fffffffffff;
const long long INF = 0x1fffffffffffffff;
const long long MOD = 998244353;
const long double EPS = 1e-9;
const long double PI = acos(-1);
 
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

template<typename T1, typename T2> istream &operator>>(istream &is, pair<T1, T2> &p){ is >> p.first >> p.second; return is; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){ os << "(" << p.first << ", " << p.second << ")"; return os; }
template<typename T> istream &operator>>(istream &is, vector<T> &v){ for(T &in : v) is >> in; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &v){ for(int i = 0; i < (int) v.size(); ++i){ os << v[i] << (i + 1 != (int) v.size() ? " " : ""); } return os; }
template <typename T, typename S> ostream &operator<<(ostream &os, const map<T, S> &mp){ for(auto &[key, val] : mp){ os << key << ":" << val << " "; } return os; }
template <typename T> ostream &operator<<(ostream &os, const set<T> &st){ auto itr = st.begin(); for(int i = 0; i < (int)st.size(); ++i){ os << *itr << (i + 1 != (int)st.size() ? " " : ""); itr++; } return os; }
template <typename T> ostream &operator<<(ostream &os, const multiset<T> &st){ auto itr = st.begin(); for(int i = 0; i < (int)st.size(); ++i){ os << *itr << (i + 1 != (int)st.size() ? " " : ""); itr++; } return os; }
template <typename T> ostream &operator<<(ostream &os, queue<T> q){ while(q.size()){ os << q.front() << " "; q.pop(); } return os; }
template <typename T> ostream &operator<<(ostream &os, deque<T> q){ while(q.size()){ os << q.front() << " "; q.pop_front(); } return os; }
template <typename T> ostream &operator<<(ostream &os, stack<T> st){ while(st.size()){ os << st.top() << " "; st.pop(); } return os; }
template <class T, class Container, class Compare> ostream &operator<<(ostream &os, priority_queue<T, Container, Compare> pq){ while(pq.size()){ os << pq.top() << " "; pq.pop(); } return os; }

template<class T, class U> inline T vin(T& vec, U n) { vec.resize(n); for(int i = 0; i < (int) n; ++i) cin >> vec[i]; return vec; }
template<class T> inline void vout(T vec, string s = "\n"){ for(auto x : vec) cout << x << s; }
template<class... T> void in(T&... a){ (cin >> ... >> a); }
void out(){ cout << '\n'; }
template<class T, class... Ts> void out(const T& a, const Ts&... b){ cout << a; (cout << ... << (cout << ' ', b)); cout << '\n'; }
template<class T, class U> void inGraph(vector<vector<T>>& G, U n, U m, bool directed = false){ G.resize(n); for(int i = 0; i < m; ++i){ int a, b; cin >> a >> b; a--, b--; G[a].push_back(b); if(!directed) G[b].push_back(a); } }

struct UnionFind{
    vector<int> par;
    vector<int> siz;
    vector<int> edg;

    UnionFind(int N) : par(N), siz(N), edg(N){
        for(int i = 0; i < N; ++i){
            par[i] = i;
            siz[i] = 1;
            edg[i] = 0;
        }
    }

    int root(int x){
        if(par[x] == x) return x;
        return par[x] = root(par[x]);
    }

    void unite(int x, int y){
        int rx = root(x);
        int ry = root(y);
        if(rx == ry){
            edg[rx]++;
            return;
        }
        par[rx] = ry;
        siz[ry] += siz[rx];
        edg[ry] += edg[rx] + 1;
    }

    bool same(int x, int y){
        int rx = root(x);
        int ry = root(y);
        return rx == ry;
    }

    long long size(int x){
        return siz[root(x)];
    }

    long long edge(int x){
        return edg[root(x)];
    }
};

ll n, m;
vector<ll> a, b, c;
ll ti;

void input(){
    in(n, m);
    a.resize(m); b.resize(m);
    rep(i, m){
        in(a[i], b[i]);
    }
    vin(c, n);
}

ll solve2(vll v){
    ll siz = v.size();
    if(siz == 0){
        return 0;
    }
    map<ll, ll> conv;
    rep(i, siz) conv[v[i]] = i;
    map<string, ll> mp;
    queue<string> q;
    string s(siz, '$');
    rep(i, siz) s[i] = c[v[i]] + '0';
    q.push(s); mp[s] = 0;
    while(q.size() && clock() - ti <= 350 * CLOCKS_PER_SEC / 100){
        string t = q.front();
        q.pop();
        rep(i, m){
            string nxt = t;
            if(conv.count(a[i]) == 0 || conv.count(b[i]) == 0) continue;
            
            if(nxt[conv[a[i]]] == '0' && nxt[conv[b[i]]] == '0'){
                continue;
            }
            if(nxt[conv[a[i]]] == '1'){
                nxt[conv[a[i]]]--;
            }else{
                nxt[conv[a[i]]]++;
            }
            if(nxt[conv[b[i]]] == '1'){
                nxt[conv[b[i]]]--;
            }else{
                nxt[conv[b[i]]]++;
            }
            if(mp.count(nxt) == 0){
                mp[nxt] = mp[t] + 1;
                q.push(nxt);
            }
        }
    }
    string ans(siz, '0');
    if(mp.count(ans) == 0){
        return -1;
    }else{
        return mp[ans];
    }
}

void solve(){
    UnionFind dsu(n);
    rep(i, m){
        a[i]--, b[i]--;
        dsu.unite(a[i], b[i]);
    }
    vector<vll> group(n);
    rep(i, n){
        group[dsu.root(i)].push_back(i);
    }
    ll ans = 0;
    rep(i, n){
        ll res = solve2(group[i]);
        if(res == -1){
            ans = -1;
            break;
        }else{
            ans += res;
        }
    }
    out(ans);
}

int main(){
    ti = clock();
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    input();
    solve();
}