3 2
1 0 1
1 2
2 3
 10 10
-1 -1 -1 -1 -1 -1 -1 -1 -1 -1
6 7
8 3
6 4
4 2
9 2
5 10
9 8
10 7
5 1
6 2

2
1
2
 0

#include <bits/stdc++.h>
using namespace std;
template <class T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}
const int mod = 1000000007, MAX = 300005, INF = 1 << 30;
vector<pair<int, int>> G[MAX];
int S[MAX];
bool use[MAX], visited[MAX];
bool ans = 1;
void DFS(int u, int p, int e) {
  visited[u] = 1;
  for (auto to : G[u]) {
    if (to.first == p) continue;
    if (visited[to.first]) continue;
    DFS(to.first, u, to.second);
  }
  if (S[u] == 1) {
    if (e == -1)
      ans = 0;
    else {
      use[e] = 1;
      S[u] ^= 1;
      if (S[p] >= 0) S[p] ^= 1;
    }
  }
}
int main() {
  std::ifstream in("text.txt");
  std::cin.rdbuf(in.rdbuf());
  cin.tie(0);
  ios::sync_with_stdio(false);
  int N, M;
  cin >> N >> M;
  for (int i = 0; i < N; i++) {
    cin >> S[i];
  }
  for (int i = 0; i < M; i++) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    G[a].push_back(make_pair(b, i));
    G[b].push_back(make_pair(a, i));
  }
  DFS(0, -1, -1);
  if (ans) {
    int cnt = 0;
    for (int i = 0; i < M; i++)
      if (use[i]) cnt++;
    cout << cnt << endl;
    for (int i = 0; i < M; i++)
      if (use[i]) cout << i + 1 << "\n";
  } else
    cout << -1 << endl;
}
