import java.io.*;
import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int m = sc.nextInt();
        ArrayList<Long> valueA = new ArrayList<>();
        ArrayList<Long> valueB = new ArrayList<>();
        for (int i = 0; i < m; i++) {
            long v = (1L << (sc.nextInt() - 1)) + (1L << (sc.nextInt() - 1));
            if (i % 2 == 0) {
                valueA.add(v);
            } else {
                valueB.add(v);
            }
        }
        long ans = 0;
        for (int i = 0; i < n; i++) {
            ans += (sc.nextLong() << i);
        }
        int sizeA = valueA.size();
        long[] dpA = new long[1 << sizeA];
        dpA[0] = ans;
        HashMap<Long, Integer> countsA = new HashMap<>();
        countsA.put(ans, 0);
        for (int i = 0; i < (1 << sizeA); i++) {
            int pop = getPop(i);
            for (int j = 0; j < sizeA; j++) {
                if ((i & (1 << j)) > 0) {
                    dpA[i] = dpA[i ^ (1 << j)] ^ valueA.get(j);
                    break;
                }
            }
            if (!countsA.containsKey(dpA[i]) || countsA.get(dpA[i]) > pop) {
                countsA.put(dpA[i], pop);
            }
        }
        int sizeB = valueB.size();
        long[] dpB = new long[1 << sizeB];
        HashMap<Long, Integer> countsB = new HashMap<>();
        countsB.put(0L, 0);
        for (int i = 0; i < (1 << sizeB); i++) {
            int pop = getPop(i);
            for (int j = 0; j < sizeB; j++) {
                if ((i & (1 << j)) > 0) {
                    dpB[i] = dpB[i ^ (1 << j)] ^ valueB.get(j);
                    break;
                }
            }
            if (!countsB.containsKey(dpB[i]) || countsB.get(dpB[i]) > pop) {
                countsB.put(dpB[i], pop);
            }
        }
        int result = Integer.MAX_VALUE;
        for (long x : countsA.keySet()) {
            if (countsB.containsKey(x)) {
                result = Math.min(result, countsA.get(x) + countsB.get(x));
            }
        }
        if (result > n) {
            System.out.println(-1);
        } else {
            System.out.println(result);
        }
    }
    
    static int getPop(int x) {
        int pop = 0;
        while (x > 0) {
            pop += x % 2;
            x >>= 1;
        }
        return pop;
        
    }
}
class Utilities {
    static String arrayToLineString(Object[] arr) {
        return Arrays.stream(arr).map(x -> x.toString()).collect(Collectors.joining("\n"));
    }
    
    static String arrayToLineString(int[] arr) {
        return String.join("\n", Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new));
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public int[] nextIntArray() throws Exception {
        return Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
    
}