#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
const long long inf = 3e18 + 5;
int add(int a, int b) { return (a += b) < mod ? a : a - mod; }
int mul(int a, int b) { return 1LL * a * b % mod; }
int sub(int a, int b) { return (a -= b) < 0 ? a + mod : a; }
int ctz(int x) { return __builtin_ctz(x); }
int clz(int x) { return __builtin_clz(x); }
const int maxn = 3e5 + 5;
int d[maxn], done[maxn], M = -1, dp[maxn];
vector<pair<int, int> > g[maxn], ng[maxn];
map<pair<int, int>, int> edg;
int dfs(int u) {
  done[u] = 1;
  int ret = 0;
  for (auto [v, i] : g[u]) {
    if (!done[v]) {
      int r = dfs(v);
      ret |= r;
      if (r == 1) {
        ng[u].emplace_back(v, i);
        ng[v].emplace_back(u, i);
      }
    }
  }
  return ret || (d[u] == 1) || (u == M);
}
vector<int> sol;
void dpdfs(int u, int p) {
  for (auto [v, i] : ng[u]) {
    if (v != p) {
      dpdfs(v, u);
      dp[u] ^= dp[v];
      if (dp[v]) sol.push_back(i);
    }
  }
  if (dp[u] == 1) {
  }
}
int main() {
  int n, m;
  cin >> n >> m;
  vector<int> ones;
  for (int i = 1; i <= n; i++) {
    cin >> d[i];
    if (d[i] == 1) ones.push_back(i);
  }
  for (int i = 0; i < m; i++) {
    int u, v;
    cin >> u >> v;
    g[u].emplace_back(v, i);
    g[v].emplace_back(u, i);
    if (d[u] == -1) M = u;
    if (d[v] == -1) M = v;
    edg[{u, v}] = i;
  }
  if (int(ones.size()) % 2 == 1 && M == -1) return cout << -1, 0;
  if (ones.empty()) return cout << 0, 0;
  int root = ones.back();
  dfs(root);
  while (ones.size()) {
    int a = ones.back();
    ones.pop_back();
    if (M != -1) {
      dp[a] ^= 1;
      dp[M] ^= 1;
      continue;
    }
    int b = ones.back();
    ones.pop_back();
    dp[a] ^= 1;
    dp[b] ^= 1;
  }
  dpdfs(root, root);
  cout << int(sol.size()) << "\n";
  for (int y : sol) {
    cout << y + 1 << " ";
  }
}
