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;
int n, m;
vector<bool> vis(345678, false);
vector<int> ans;
bool DFSdoit(int root, vector<int>& d, vector<vector<pair<int, int> > >& G) {
  vis[root] = true;
  bool edge = d[root] == 1;
  for (pair<int, int> v : G[root])
    if (!vis[v.first])
      if (DFSdoit(v.first, d, G)) {
        edge = !edge;
        ans.push_back(v.second);
      }
  return edge;
}
bool BFSdoit(int root, vector<int>& d, vector<vector<pair<int, int> > >& G) {
  vis[root] = true;
}
void doit(int root, vector<int>& d, vector<vector<pair<int, int> > >& G) {
  vector<vector<int> > levels(n);
  levels[0].push_back(root);
  vector<vector<pair<int, int> > > T(n);
  vis[root] = true;
  for (int i = 0; i + 1 < n; i++)
    for (int v : levels[i])
      for (pair<int, int> u : G[v])
        if (!vis[u.first]) {
          vis[u.first] = true;
          T[v].push_back(u);
          levels[i + 1].push_back(u.first);
        }
  vector<bool> f(n, false);
  int k = 0;
  for (int i = n - 1; i >= 0; i--)
    for (int v : levels[i]) {
      f[v] = d[v] == 1;
      for (pair<int, int> u : T[v])
        if (f[u.first]) {
          f[v] = !f[v];
          ans.push_back(u.second);
        }
    }
  cout << int((ans).size()) << endl;
  for (int x : ans) cout << x << " ";
}
int main() {
  cin >> n >> m;
  vector<int> d(n);
  int root = 0;
  bool cnt = true, neg = false;
  for (int i = 0; i < n; i++) {
    cin >> d[i];
    if (d[i] == 1) cnt = !cnt;
    if (d[i] == -1) {
      neg = true;
      root = i;
    }
  }
  if (!cnt && !neg) {
    cout << -1 << endl;
    return 0;
  }
  vector<vector<pair<int, int> > > G(n);
  for (int i = 1; i <= m; i++) {
    int u, v;
    cin >> u >> v;
    u--;
    v--;
    pair<int, int> p(v, i);
    G[u].push_back(p);
    pair<int, int> q(u, i);
    G[v].push_back(q);
  }
  doit(root, d, G);
  return 0;
}
