#include <stdio.h>
#include <stdlib.h>

int cmp_ll_alt (const void *a, const void *b) {
  long long *a_ = (long long *)a;
  long long *b_ = (long long *)b;
  
  if (a_[0] < b_[0]) {
    return -1;
  }
  
  if (a_[0] > b_[0]) {
    return 1;
  }
  
  if (a_[1] < b_[1]) {
    return 1;
  }
  
  if (a_[1] > b_[1]) {
    return -1;
  }
  
  return 0;
}

int main () {
  int n = 0;
  int m = 0;
  long long a[40] = {};
  long long b[40] = {};
  long long c = 0LL;
  
  int res = 0;
  
  int ans = 0;
  
  long long cbit = 0LL;
  long long half[1048576][2] = {};
  
  res = scanf("%d", &n);
  res = scanf("%d", &m);
  for (int i = 0; i < m; i++) {
    res = scanf("%lld", a+i);
    res = scanf("%lld", b+i);
    a[i] -= 1LL;
    b[i] -= 1LL;
  }
  for (int i = 0; i < n; i++) {
    res = scanf("%lld", &c);
    cbit |= (c<<((long long)i));
  }
  
  ans = m+1;
  
  for (int i = 0; i < (1<<(m/2)); i++) {
    for (int j = 0; j < m/2; j++) {
      if ((i&(1<<j)) > 0) {
        half[i][1] += 1LL;
        half[i][0] ^= (1LL<<a[j]);
        half[i][0] ^= (1LL<<b[j]);
      }
    }
  }
  
  qsort(half, (1<<(m/2)), sizeof(long long)*2, cmp_ll_alt);
  
  for (int i = 0; i < (1<<(m-m/2)); i++) {
    long long hbit = 0LL;
    int cnt = 0;
    int idx[2] = { 0, (1<<m/2) };
    for (int j = 0; j < m-m/2; j++) {
      if ((i&(1<<j)) > 0) {
        cnt++;
        hbit ^= (1LL<<a[j+m/2]);
        hbit ^= (1LL<<b[j+m/2]);
      }
    }
    while (idx[1] - idx[0] > 1) {
      int nxt = (idx[0]+idx[1])/2;
      if (half[nxt][0] <= (cbit^hbit)) {
        idx[0] = nxt;
      } else {
        idx[1] = nxt;
      }
    }
    if (half[idx[0]][0] == (cbit^hbit) && ans > cnt+((int)half[idx[0]][1])) {
      ans = cnt+((int)half[idx[0]][1]);
    }
  }
  
  if (ans > m) {
    printf("-1\n");
    return 0;
  }
  
  printf("%d\n", ans);
  return 0;
}