#include <bits/stdc++.h>
using namespace std;
mt19937 rnd(rand());
const int MOD = 1e9 + 7;
const long long BIG_MOD = 1e18 + 7;
const int MAXN = 3e5 + 7;
vector<pair<int, int> > g[MAXN];
int d[MAXN];
vector<int> ans;
bool used[MAXN];
bool dfs(int u, int last) {
  used[u] = true;
  int _xor = 0;
  for (pair<int, int> v : g[u]) {
    if (!used[v.first]) {
      _xor ^= dfs(v.first, v.second);
    }
  }
  if (last != -1 && _xor != d[u]) {
    ans.push_back(last);
  }
  return _xor != d[u];
}
signed main() {
  cout.precision(20);
  ios_base::sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  bool good = false;
  int _xor = 0;
  for (int i = 0; i < n; ++i) {
    cin >> d[i];
    if (d[i] == -1) {
      good = true;
    } else {
      _xor ^= d[i];
    }
  }
  if (!good && _xor) {
    cout << "-1\n";
    return 0;
  }
  if (good && _xor) {
    for (int i = 0; i < n; ++i) {
      if (d[i] == -1) {
        d[i] = 1;
        break;
      }
    }
  }
  for (int i = 0; i < n; ++i) {
    if (d[i] == -1) {
      d[i] = 0;
    }
  }
  int u, v;
  for (int i = 0; i < m; ++i) {
    cin >> u >> v;
    g[u - 1].push_back({v - 1, i});
    g[v - 1].push_back({u - 1, i});
  }
  dfs(0, -1);
  cout << ans.size() << '\n';
  for (int elem : ans) {
    cout << elem + 1 << ' ';
  }
  return 0;
}
