#include <iostream>
#include <vector>
using namespace std;

// 最大重み一般マッチング
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/maximum_weighted_matching.hpp>

using EdgeProperty = boost::property<boost::edge_weight_t, long long, boost::property<boost::edge_index_t, int>>;
using my_graph = boost::adjacency_list<boost::vecS, boost::vecS, boost::undirectedS, boost::no_property, EdgeProperty>;

void No() {
    puts("-1");
    exit(0);
}

int main() {
    int N, M;
    cin >> N >> M;
    constexpr int inf = 1 << 20;
    vector dist(N, vector<int>(N, inf));
    for (int i = 0; i < N; ++i) dist.at(i).at(i) = 0;

    while (M--) {
        int a, b;
        cin >> a >> b, --a, --b, dist.at(a).at(b) = dist.at(b).at(a) = 1;
    }

    for (int k = 0; k < N; ++k) for (int i = 0; i < N; ++i) {
        for (int j = 0; j < N; ++j) dist.at(i).at(j) = min(dist.at(i).at(j), dist.at(i).at(k) + dist.at(k).at(j));
    }

    vector<int> vs;
    for (int i = 0, ci; cin >> ci, i < N; ++i) {
        if (ci) vs.push_back(i);
    }
    const int n_vertices = vs.size();

    if (n_vertices % 2) No();

    my_graph g(n_vertices);
    for (int i = 0; i < n_vertices; ++i) {
        for (int j = 0; j < i; ++j) {
            if (auto w = dist.at(vs.at(i)).at(vs.at(j)); w < inf) add_edge(i, j, EdgeProperty(N - w), g);
        }
    }

    vector<boost::graph_traits<my_graph>::vertex_descriptor> mate1(n_vertices);
    maximum_weighted_matching(g, &mate1[0]);

    auto sz = matching_size(g, &mate1[0]);
    auto ret = matching_weight_sum(g, &mate1[0]);

    if (sz * 2 < n_vertices) No();
    cout << N * vs.size() / 2 - ret << endl;
}