#include <bits/stdc++.h>
using namespace std;
template <typename T>
using vc = vector<T>;
template <typename T, typename X>
using pr = pair<T, X>;
const long long int MOD = 1e9 + 7;
const long double PI = 3.14159265;
long long int powerWithMod(long long int base, long long int exponent,
                           long long int modulus = LLONG_MAX) {
  long long int result = 1;
  base %= modulus;
  while (exponent > 0) {
    if (exponent % 2 == 1) result = (result * base) % modulus;
    exponent >>= 1;
    base = (base * base) % modulus;
  }
  return result;
}
long long int modInverse(long long int a, long long int m = MOD) {
  return powerWithMod(a, m - 2, m);
}
int n, m, a[312345], cnt, f;
vc<int> adj[312345];
vc<bool> visited(312345);
set<int> ans;
map<pr<int, int>, int> ed;
bool dfs(int v, int par) {
  visited[v] = true;
  int curr = 0;
  for (auto& x : adj[v])
    if (!visited[x]) curr ^= dfs(x, v);
  if (a[v] == -1) a[v] = 0;
  if (a[v] != curr) ans.insert(ed[{min(v, par), max(v, par)}]);
  return a[v] != curr;
}
int main() {
  ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  cin >> n >> m;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    if (a[i] == 1)
      cnt ^= 1;
    else if (a[i] == -1)
      f = 1;
  }
  if (!f and cnt) {
    cout << "-1\n";
    return 0;
  }
  if (cnt) {
    for (int i = 1; i <= n; i++)
      if (a[i] == -1) {
        a[i] = 1;
        break;
      }
  }
  for (int i = 1; i <= m; i++) {
    int x, y;
    cin >> x >> y;
    adj[x].push_back(y);
    adj[y].push_back(x);
    ed[{min(x, y), max(x, y)}] = i;
  }
  dfs(1, 0);
  cout << ans.size() << "\n";
  for (auto& x : ans) cout << x << " ";
  cout << "\n";
  return 0;
}
