#include <bits/stdc++.h>
using namespace std;
vector<int> v[300005];
int n, m;
int value[300005];
int visit[300005];
int cnt[300005];
int test[300005][2];
int test2[300005];
int root;
int recall(int node) {
  int si = v[node].size();
  int i;
  int cntchild = 0;
  for (i = 0; i < si / 2; i++) {
    int ne = v[node][2 * i];
    int en = v[node][2 * i + 1];
    if (visit[ne] == 0) {
      visit[ne] = 1;
      int tmp = recall(ne);
      if (tmp & 1) cnt[en] ^= 1;
      cntchild += tmp;
    }
  }
  if (value[node] == 1) cntchild++;
  return cntchild;
}
int main(void) {
  int i;
  scanf("%d %d", &n, &m);
  for (i = 1; i <= n; i++) {
    scanf("%d", &value[i]);
    if (value[i] == -1) root = i;
  }
  if (root == 0) {
    for (i = 1; i <= n; i++) {
      if (value[i] == 1) root = i;
    }
  }
  if (root == 0)
    printf("0");
  else {
    int x, y;
    for (i = 1; i <= m; i++) {
      scanf("%d %d", &x, &y);
      test[i][0] = x;
      test[i][1] = y;
      v[x].push_back(y);
      v[x].push_back(i);
      v[y].push_back(x);
      v[y].push_back(i);
    }
    visit[root] = 1;
    recall(root);
    for (i = 1; i <= m; i++) {
      if (cnt[i] == 1) {
        test2[test[i][0]]++;
        test2[test[i][1]]++;
      }
    }
    for (i = 1; i <= n; i++) {
      if (value[i] == -1 || value[i] == (test2[i] % 2)) continue;
      break;
    }
    if (i != n + 1)
      printf("-1");
    else {
      int ans = 0;
      for (i = 1; i <= m; i++) ans += cnt[i];
      printf("%d\n", ans);
      for (i = 1; i <= m; i++) {
        if (cnt[i]) printf("%d\n", i);
      }
    }
  }
}
