#include <bits/stdc++.h>
using namespace std;
const int MAXN = 300100;
struct edge {
  int v;
  int id;
  edge* next;
} pool[2 * MAXN], *h[MAXN];
int n, m, d[MAXN], p[MAXN], pid[MAXN], top = -1;
int ans[MAXN], vis[MAXN];
void addedge(int u, int v, int id) {
  edge *tmp = &pool[++top], *tmq = &pool[++top];
  tmp->v = v;
  tmp->next = h[u];
  tmp->id = id;
  h[u] = tmp;
  tmq->v = u;
  tmq->next = h[v];
  tmq->id = id;
  h[v] = tmq;
}
void dfs(int u) {
  for (edge* tmp = h[u]; tmp != NULL; tmp = tmp->next) {
    int v = tmp->v;
    if (p[v] == 0) {
      p[v] = u;
      pid[v] = tmp->id;
      dfs(v);
    }
  }
}
int dfs_2(int u) {
  if (vis[u] == true) return 0;
  vis[u] = true;
  int tot = 0;
  if (d[u] == 1) tot = 1;
  for (edge* tmp = h[u]; tmp != NULL; tmp = tmp->next) {
    int v = tmp->v;
    if (p[v] == u) {
      tot += dfs_2(v);
    }
  }
  ans[pid[u]] += tot;
  return tot;
}
void init() {
  int x1, x2;
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; i++) scanf("%d", &d[i]);
  for (int i = 1; i <= m; i++) {
    scanf("%d%d", &x1, &x2);
    addedge(x1, x2, i);
  }
  int cnt = 0;
  for (int i = 1; i <= n; i++)
    if (d[i] == 1) cnt++;
  if (cnt % 2 == 1) {
    bool flag = false;
    for (int i = 1; i <= n; i++) {
      if (d[i] == -1) {
        d[i] = 1;
        flag = true;
        break;
      }
    }
    if (flag == false) {
      printf("-1\n");
      return;
    }
  }
  p[1] = -1;
  dfs(1);
  dfs_2(1);
  cnt = 0;
  for (int i = 1; i <= m; i++) cnt += (ans[i] % 2);
  printf("%d\n", cnt);
  for (int i = 1; i <= m; i++)
    if (ans[i] % 2 == 1) printf("%d\n", i);
}
int main(int argc, char** argv) {
  init();
  return 0;
}
