#include <bits/stdc++.h>
using namespace std;
int a[300005];
bool up[300005];
int num[300005];
struct edge {
  int y;
  int id;
  edge* next;
};
edge* li[300005];
edge* new_edge() {
  static edge a[600005];
  static int top = 0;
  return &a[top++];
}
void inserts(int x, int y, int z) {
  edge* t = new_edge();
  t->y = y;
  t->id = z;
  t->next = li[x];
  li[x] = t;
}
void insert_edge(int x, int y, int z) {
  inserts(x, y, z);
  inserts(y, x, z);
}
int fa[300005];
bool vis[300005];
void dfs(int x) {
  vis[x] = true;
  edge* t;
  for (t = li[x]; t != 0; t = t->next) {
    if (vis[t->y]) continue;
    fa[t->y] = x;
    num[t->y] = t->id;
    dfs(t->y);
  }
}
void dfs2(int x) {
  vis[x] = false;
  edge* t;
  for (t = li[x]; t != 0; t = t->next) {
    if ((fa[t->y] == x) && (vis[t->y])) {
      dfs2(t->y);
      if (up[t->y]) up[x] ^= 1;
    }
  }
}
int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  int i;
  int ans = 0;
  for (i = 0; i < n; i++) {
    scanf("%d", &a[i]);
    if (a[i] == -1) ans = -1;
    if (ans != -1) ans ^= a[i];
  }
  for (i = 0; i < m; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    x--;
    y--;
    insert_edge(x, y, i + 1);
  }
  if (ans == 1) {
    puts("-1");
    return 0;
  }
  memset(fa, -1, sizeof(fa));
  dfs(0);
  ans = 0;
  for (i = 0; i < n; i++) {
    if (a[i] == 1) {
      up[i] = 1;
      ans ^= 1;
    }
  }
  if (ans == 1) {
    for (i = 0; i < n; i++) {
      if (a[i] == -1) {
        up[i] = 1;
        break;
      }
    }
  }
  dfs2(0);
  int sum = 0;
  for (i = 1; i < n; i++) {
    if (up[i]) {
      sum++;
    }
  }
  printf("%d\n", sum);
  for (i = 1; i < n; i++) {
    if (up[i]) {
      printf("%d\n", num[i]);
    }
  }
  return 0;
}
