#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <complex>
#include <deque>
#include <forward_list>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#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 namespace boost;

typedef property<edge_weight_t, float, property<edge_index_t, int>> EdgeProperty;
typedef adjacency_list<vecS, vecS, undirectedS, no_property, EdgeProperty> my_graph;

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();

    graph_traits<my_graph>::vertex_iterator vi, vi_end;
    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);
        }
    }

    graph_traits<my_graph>::vertex_descriptor mate1(n_vertices);
    maximum_weighted_matching(g, &mate1);

    auto sz = matching_size(g, &mate1);
    int ret = matching_weight_sum(g, &mate1);
    if (sz * 2 < n_vertices) No();
    ret = N * vs.size() / 2 - ret;
    cout << ret << endl;
}