import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }




void main() {
  try {
    for (; ; ) {
      const N = readInt;
      const M = readInt;
      auto A = new int[M];
      auto B = new int[M];
      foreach (i; 0 .. M) {
        A[i] = readInt - 1;
        B[i] = readInt - 1;
      }
      auto C = new int[N];
      foreach (u; 0 .. N) {
        C[u] = readInt;
      }
      
      long ini;
      foreach (u; 0 .. N) if (C[u]) {
        ini |= 1L << u;
      }
      
      const half = M / 2;
      alias Entry = Tuple!(long, "on", int, "cost");
      auto fs = new Entry[1 << half];
      foreach (i; 0 .. half) {
        foreach (h; 0 .. 1 << i) {
          fs[h | 1 << i].on = fs[h].on ^ (1L << A[i]) ^ (1L << B[i]);
          fs[h | 1 << i].cost = fs[h].cost + 1;
        }
      }
      fs.sort;
      auto gs = new Entry[1 << (M - half)];
      foreach (i; 0 .. M - half) {
        foreach (h; 0 .. 1 << i) {
          gs[h | 1 << i].on = gs[h].on ^ (1L << A[half + i]) ^ (1L << B[half + i]);
          gs[h | 1 << i].cost = gs[h].cost + 1;
        }
      }
      int ans = M + 1;
      foreach (ref g; gs) {
        const tar = ini ^ g.on;
        const pos = fs.lowerBound(Entry(tar, -1));
        if (pos < fs.length && fs[pos].on == tar) {
          chmin(ans, fs[pos].cost + g.cost);
        }
      }
      writeln((ans <= M) ? ans : -1);
    }
  } catch (EOFException e) {
  }
}