#include <bits/stdc++.h>
using namespace std;
string itos(int x) {
  stringstream ss;
  ss << x;
  return ss.str();
}
int n, m, d[300010], vis[300010];
pair<int, int> a[300010];
vector<int> e[300010], res;
int dfs(int now) {
  if (vis[now]) return 0;
  vis[now] = 1;
  d[now] = (d[now] == 1);
  for (auto x : e[now]) {
    int y = (a[x].first == now ? a[x].second : a[x].first);
    if (dfs(y)) {
      res.push_back((x));
      d[now] ^= 1;
    }
  }
  return d[now] == 1;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n >> m;
  for (int i = 0; i < n; i++) cin >> d[i];
  for (int i = 0, u, v; i < m;) {
    cin >> u >> v;
    a[++i] = make_pair((--u), (--v));
    e[u].push_back((i)), e[v].push_back((i));
  }
  int cnt1, free;
  cnt1 = count_if(d, d + 300010, [](int x) { return x == 1; }),
  free = count_if(d, d + 300010, [](int x) { return x == -1; });
  if (cnt1 % 2 && not free) {
    cout << -1 << endl;
    return 0;
  }
  if (cnt1 % 2) *find(d, d + 300010, -1) = 1;
  dfs(0);
  cout << res.size() << endl;
  for (int i = 0; i < res.size(); i++)
    cout << res[i] << (i + 1 == res.size() ? '\n' : ' ');
  return 0;
}
