#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using mint = modint998244353;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repf(i, n, flag) for (int i = 0; i < (int)(n) && flag; i++)
#define all(v) v.begin(), v.end()


const int INF = 1e9;

int main() {
    int n, m;
    cin >> n >> m;
    vector dp(n, vector<int>(n, INF));
    rep(i, m) {
        int a, b;
        cin >> a >> b;
        a--; b--;
        dp[a][b] = dp[b][a] = 1;
    }
    int cnt = 0;
    vector<int> c(n);
    rep(i, n) {
        cin >> c[i];
        if(c[i] == 1) cnt++;
    }

    rep(k, n) rep(i, n) rep(j, n) dp[i][j] = min(dp[i][j], dp[i][k] + dp[k][j]);

    mcf_graph<int, int> g(2*n+2);
    int s = 2*n, t = s + 1;
    rep(i, n) g.add_edge(s, i, 1, 0);
    rep(i, n) g.add_edge(n+i, t, 1, 0);
    rep(i, n) rep(j, n) {
        if(i == j) continue;
        if(c[i] == 0) continue;
        if(c[j] == 0) continue;
        if(dp[i][j] >= INF) continue;
        g.add_edge(i, n+j, 1, dp[i][j]);
    }
    auto res = g.flow(s, t);
    if(res.first < cnt) cout << -1 << endl;
    else cout << res.second / 2 << endl;
}