#include <bits/stdc++.h>
using namespace std;
namespace mine {
long long qread() {
  long long ans = 0, f = 1;
  char c = getchar();
  while (c < '0' or c > '9') {
    if (c == '-') f = -1;
    c = getchar();
  }
  while ('0' <= c and c <= '9') ans = ans * 10 + c - '0', c = getchar();
  return ans * f;
}
void write(long long num) {
  if (num < 0) putchar('-'), num = -num;
  if (num >= 10) write(num / 10);
  putchar('0' + num % 10);
}
void write1(long long num) {
  write(num);
  putchar(' ');
}
void write2(long long num) {
  write(num);
  putchar('\n');
}
template <typename T>
void chmax(T &x, const T y) {
  x = (x > y ? x : y);
}
template <typename T>
void chmin(T &x, const T y) {
  x = (x < y ? x : y);
}
long long gcd(long long x, long long y) { return y ? gcd(y, x % y) : x; }
const int INF = 0x3f3f3f3f;
const int MOD = 998244353;
int mm(const int x) { return x >= MOD ? x - MOD : x; }
template <typename T>
void add(T &x, const int &y) {
  x = (x + y >= MOD ? x + y - MOD : x + y);
}
long long qpower(long long x, long long e, int mod = MOD) {
  long long ans = 1;
  while (e) {
    if (e & 1) ans = ans * x % mod;
    x = x * x % mod;
    e >>= 1;
  }
  return ans;
}
long long invm(long long x) { return qpower(x, MOD - 2); }
const int N = 1e6 + 10;
vector<int> to[N];
map<int, int> id[N];
bool vis[N];
int d[N];
vector<int> ans;
void dfs(int x) {
  vis[x] = 1;
  for (auto y : to[x])
    if (!vis[y]) {
      dfs(y);
      if (d[y] == 1) {
        ans.push_back(id[x][y]);
        if (d[x] >= 0) d[x] ^= 1;
      }
    }
}
void main() {
  int n = qread(), m = qread(), sum = 0, bk = 0;
  for (int i = (1), I = (n); i <= I; i++) {
    d[i] = qread();
    if (d[i] != -1)
      sum ^= d[i];
    else
      bk = i;
  }
  if (sum and !bk) {
    puts("-1");
    return;
  }
  for (int i = (1), I = (m); i <= I; i++) {
    int x = qread(), y = qread();
    to[x].push_back(y), to[y].push_back(x);
    id[x][y] = id[y][x] = i;
  }
  dfs(bk == 0 ? 1 : bk);
  write2(((int)(ans).size()));
  for (auto t : ans) write2(t);
}
};  // namespace mine
signed main() {
  srand(time(0));
  mine::main();
}
