import java.util.*;

@SuppressWarnings("unused")
public class Main {

  private static void solve() {
    int n = ni();
    int m = ni();
    int[] a = new int[m];
    int[] b = new int[m];
    for (int i = 0; i < m; i++) {
      a[i] = ni() - 1;
      b[i] = ni() - 1;
    }
    int[] c = na(n);

    // long[] dp = func(a, b, c, 0, m);

    // int ret = Integer.MAX_VALUE / 2;
    // for (int i = 0; i < dp.length; i ++) {
    //   if (dp[i] == 0) {
    //     ret = Math.min(ret, Integer.bitCount(i));
    //   }
    // }
    // System.out.println(ret == Integer.MAX_VALUE / 2 ? -1 : ret);


    long[] dp1 = func(a, b, c, 0, m / 2);
    long[] dp2 = func(a, b, c, m / 2, m);

    Map<Long, Integer> map = new HashMap<>();
    for (int i = 0; i < dp2.length; i ++) {
      long state = dp2[i];
      int cnt = Integer.bitCount(i);

      int min = map.getOrDefault(state, Integer.MAX_VALUE / 2);
      map.put(state, Math.min(min, cnt));
    }

    int m1 = m / 2;

    int ret = Integer.MAX_VALUE;

    long init = 0;
    for (int i = 0; i < n; i++) {
      if (c[i] == 1) {
        init |= 1L << i;
      }
    }

    for (int i = 0; i < 1 << m1; i ++) {
      long k = dp1[i] ^ init;

      ret = Math.min(ret, Integer.bitCount(i) + map.getOrDefault(k, Integer.MAX_VALUE / 2));
    }

    System.out.println(ret >= Integer.MAX_VALUE / 2 ? -1 : ret);
  }


  private static long[] func(int[] a, int[] b, int[] c, int from, int to) {
    int m = to - from;
    long[] dp = new long[1 << m];

    long init = 0;
    int n = c.length;
    for (int i = 0; i < n; i++) {
      if (c[i] == 1) {
        init |= 1L << i;
      }
    }

    for (int i = 0; i < (1 << m); i++) {
      long v = init;

      for (int j = 0; j < m; j++) {
        if ((i >> j & 1) == 1) {
          v ^= 1 << a[j + from];
          v ^= 1 << b[j + from];
        }
      }
      dp[i] = v;
    }

    return dp;
  }

  public static int[][] packU(int n, int[] from, int[] to) {
    return packU(n, from, to, from.length);
  }

  public static int[][] packU(int n, int[] from, int[] to, int sup) {
    int[][] g = new int[n][];
    int[] p = new int[n];
    for (int i = 0; i < sup; i++)
      p[from[i]]++;
    for (int i = 0; i < sup; i++)
      p[to[i]]++;
    for (int i = 0; i < n; i++)
      g[i] = new int[p[i]];
    for (int i = 0; i < sup; i++) {
      g[from[i]][--p[from[i]]] = to[i];
      g[to[i]][--p[to[i]]] = from[i];
    }
    return g;
  }

  public static void main(String[] args) {
    new Thread(null, new Runnable() {
      @Override
      public void run() {
        long start = System.currentTimeMillis();
        String debug = args.length > 0 ? args[0] : null;
        if (debug != null) {
          try {
            is = java.nio.file.Files.newInputStream(java.nio.file.Paths.get(debug));
          } catch (Exception e) {
            throw new RuntimeException(e);
          }
        }
        reader = new java.io.BufferedReader(new java.io.InputStreamReader(is), 32768);
        solve();
        out.flush();
        tr((System.currentTimeMillis() - start) + "ms");
      }
    }, "", 64000000).start();
  }

  private static java.io.InputStream is = System.in;
  private static java.io.PrintWriter out = new java.io.PrintWriter(System.out);
  private static java.util.StringTokenizer tokenizer = null;
  private static java.io.BufferedReader reader;

  public static String next() {
    while (tokenizer == null || !tokenizer.hasMoreTokens()) {
      try {
        tokenizer = new java.util.StringTokenizer(reader.readLine());
      } catch (Exception e) {
        throw new RuntimeException(e);
      }
    }
    return tokenizer.nextToken();
  }

  private static double nd() {
    return Double.parseDouble(next());
  }

  private static long nl() {
    return Long.parseLong(next());
  }

  private static int[] na(int n) {
    int[] a = new int[n];
    for (int i = 0; i < n; i++)
      a[i] = ni();
    return a;
  }

  private static char[] ns() {
    return next().toCharArray();
  }

  private static long[] nal(int n) {
    long[] a = new long[n];
    for (int i = 0; i < n; i++)
      a[i] = nl();
    return a;
  }

  private static int[][] ntable(int n, int m) {
    int[][] table = new int[n][m];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        table[i][j] = ni();
      }
    }
    return table;
  }

  private static int[][] nlist(int n, int m) {
    int[][] table = new int[m][n];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        table[j][i] = ni();
      }
    }
    return table;
  }

  private static int ni() {
    return Integer.parseInt(next());
  }

  private static void tr(Object... o) {
    if (is != System.in)
      System.out.println(java.util.Arrays.deepToString(o));
  }
}