#include <bits/stdc++.h>
using namespace std;
const int N = 300005;
const int mod = 1e9 + 7;
int root, ne[N * 2], son[N], ed[N * 2], siz[N], a[N], n, m, s, x, y, l, num;
bool f[N], ans[N];
void dfs(int x) {
  int l = son[x], y;
  if (a[x] == 1) siz[x] = 1;
  while (l > 0) {
    y = ed[l];
    if (!f[y]) {
      f[y] = 1;
      dfs(y);
      ans[(l + 1) / 2] ^= (siz[y] % 2);
      siz[x] += siz[y];
    }
    l = ne[l];
  }
}
int main() {
  scanf("%d%d", &n, &m);
  for (int i = (1); i < (n + 1); i++) {
    scanf("%d", &a[i]);
    if (a[i] == 1)
      s++;
    else if (a[i] == -1)
      root = i;
  }
  if (s & 1 && !root) {
    printf("-1");
    return 0;
  }
  for (int i = (1); i < (m + 1); i++) {
    scanf("%d%d", &x, &y);
    l++;
    ne[l] = son[x];
    son[x] = l;
    ed[l] = y;
    l++;
    ne[l] = son[y];
    son[y] = l;
    ed[l] = x;
  }
  if (root) {
    f[root] = 1;
    dfs(root);
  } else {
    f[1] = 1;
    dfs(1);
  }
  for (int i = (1); i < (m + 1); i++)
    if (ans[i]) num++;
  printf("%d\n", num);
  for (int i = (1); i < (m + 1); i++)
    if (ans[i]) printf("%d\n", i);
  return 0;
}
