Problem: Leha plays a computer game, where is on each level is given a connected graph with n vertices and m edges. Graph can contain multiple edges, but can not contain self loops. Each vertex has an integer di, which can be equal to 0, 1 or  - 1. To pass the level, he needs to find a «good» subset of edges of the graph or say, that it doesn't exist. Subset is called «good», if by by leaving only edges from this subset in the original graph, we obtain the following: for every vertex i, di = - 1 or it's degree modulo 2 is equal to di. Leha wants to pass the game as soon as possible and ask you to help him. In case of multiple correct answers, print any of them.

Input

The first line contains two integers n, m (1 ≤ n ≤ 3·105, n - 1 ≤ m ≤ 3·105) — number of vertices and edges.

The second line contains n integers d1, d2, ..., dn ( - 1 ≤ di ≤ 1) — numbers on the vertices.

Each of the next m lines contains two integers u and v (1 ≤ u, v ≤ n) — edges. It's guaranteed, that graph in the input is connected.

Output

Print  - 1 in a single line, if solution doesn't exist. Otherwise in the first line k — number of edges in a subset. In the next k lines indexes of edges. Edges are numerated in order as they are given in the input, starting from 1.

Examples

Input

1 0
1


Output

-1


Input

4 5
0 0 0 -1
1 2
2 3
3 4
1 4
2 4


Output

0


Input

2 1
1 1
1 2


Output

1
1


Input

3 3
0 -1 1
1 2
2 3
1 3


Output

1
2

Note

In the first sample we have single vertex without edges. It's degree is 0 and we can not get 1.

Solution (in JAVA):

Solution:
import java.io.*;
import java.util.*;

public class q4 {
    public static MyScanner in = new MyScanner();
    public static PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out), true);
    public static MyViewer view = new MyViewer();
    public static BufferedWriter log = new BufferedWriter(new OutputStreamWriter(System.out));
    public static Random rand = new Random(System.currentTimeMillis());

    public static class Pair<A, B> {
        private final A first;
        private final B second;

        public Pair(A first, B second) {
            super();
            this.first = first;
            this.second = second;
        }

        public int hashCode() {
            int hashFirst = first != null ? first.hashCode() : 0;
            int hashSecond = second != null ? second.hashCode() : 0;

            return (hashFirst + hashSecond) * hashSecond + hashFirst;
        }

        public boolean equals(Object other) {
            if (other instanceof Pair) {
                Pair otherPair = (Pair) other;
                return
                        ((this.first == otherPair.first ||
                                (this.first != null && otherPair.first != null &&
                                        this.first.equals(otherPair.first))) &&
                                (this.second == otherPair.second ||
                                        (this.second != null && otherPair.second != null &&
                                                this.second.equals(otherPair.second))));
            }

            return false;
        }

        public String toString() {
            return "(" + first + ", " + second + ")";
        }

        public A getFirst() {
            return first;
        }

        public B getSecond() {
            return second;
        }
    }

    public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;
        private boolean randomInput = false;
        private Random rand;

        void randomInput(boolean r) {
            randomInput = r;
            rand = new Random(System.currentTimeMillis());
            //rand = new Random(42);
        }

        public MyScanner() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        public MyScanner(InputStream is) {
            br = new BufferedReader(new InputStreamReader(is));
        }

        public String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        int nextInt(int val) {
            return randomInput ? val : Integer.parseInt(next());
        }

        int nextInt(int low, int high) {
            if (randomInput) {
                return rand.nextInt(high - low + 1) + low;
            } else {
                return Integer.parseInt(next());
            }
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        long nextLong(long val) {
            return randomInput ? val : Long.parseLong(next());
        }

        long nextLong(long low, long high) {
            if (randomInput) {
                return low + ((long) (rand.nextDouble() * (high - low + 1)));
            } else {
                return Long.parseLong(next());
            }
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        int[] arrayInt(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++) {
                a[i] = nextInt();
            }
            return a;
        }

        int[] arrayInt(int n, int low, int high) {
            int[] a = new int[n];
            if (randomInput) {
                for (int i = 0; i < n; i++) {
                    a[i] = rand.nextInt(high - low + 1) + low;
                }
            } else {
                for (int i = 0; i < n; i++) {
                    a[i] = nextInt();
                }
            }
            return a;
        }

        ArrayList<Integer> list(int n) {
            ArrayList<Integer> a = new ArrayList<Integer>(n);
            for (int i = 0; i < n; i++) {
                a.add(nextInt());
            }
            return a;
        }

        ArrayList<Integer> list(int n, int low, int high) {
            ArrayList<Integer> a = new ArrayList<Integer>(n);
            if (randomInput) {
                for (int i = 0; i < n; i++) {
                    a.add(rand.nextInt(high - low + 1) + low);
                }
            } else {
                for (int i = 0; i < n; i++) {
                    a.add(nextInt());
                }
            }
            return a;
        }

        long[] arrayLong(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++) {
                a[i] = nextLong();
            }
            return a;
        }

        long[] arrayLong(int n, long low, long high) {
            long[] a = new long[n];
            if (randomInput) {
                for (int i = 0; i < n; i++) {
                    double r = rand.nextDouble();
                    a[i] = (long) (r * (double) (high - low + 1)) + low;
                    if (a[i] == 0) {
                        out.println("Ouch : " + r);
                    }
                }
            } else {
                for (int i = 0; i < n; i++) {
                    a[i] = nextLong();
                }
            }
            return a;
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }

        void close() {
            try {
                br.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        ArrayList<ArrayList<Integer>> randomTree(int n) {
            ArrayList<ArrayList<Integer>> edges = new ArrayList<>();
            for (int i = 0; i < n; i++) {
                edges.add(new ArrayList<>());
            }

            for (int i = 1; i < n; i++) {
                int par = rand.nextInt(i);
                edges.get(par).add(i);
            }
            return edges;
        }
    }

    static class MyViewer {
        static boolean print = true;

        public void on() {
            print = true;
        }

        public void off() {
            print = false;
        }

        public <T extends List> void list(T a) {
            if (!print) return;
            out.print("List: [" + a.get(0));
            for (int i = 1; i < a.size(); i++) {
                out.print(", " + a.get(i));
            }
            out.println("] Len: " + a.size());
        }

        public <T> void array(T[] a) {
            if (!print) return;
            out.print("Array: [" + a[0]);
            for (int i = 1; i < a.length; i++) {
                out.print(", " + a[i]);
            }
            out.println("] Len: " + a.length);
        }

        public void array(boolean[] a) {
            if (!print) return;
            out.print("boolean[] Len: " + a.length + " [");
            for (boolean x : a) {
                out.print(x + ", ");
            }
            out.println("\b\b]");
        }

        public void array(int[] a) {
            if (!print) return;
            out.print("int[] Len: " + a.length + " [");
            for (int x : a) {
                out.print(x + ", ");
            }
            out.println("\b\b]");
        }

        public void array(long[] a) {
            if (!print) return;
            out.print("long Array: [");
            for (long x : a) {
                out.print(x + ", ");
            }
            out.println("\b\b] Len: " + a.length);
        }

        public void matrix(int[][] a, int cutoff) {
            if (cutoff == 0)
                cutoff = Integer.MAX_VALUE;
            for (int i = 0; i < a.length; i++) {
                if (i < cutoff) {
                    printMatrixRow(a[i], cutoff);
                } else {
                    out.println("     ...");
                    printMatrixRow(a[a.length - 1], cutoff);
                    break;
                }
            }
        }

        public void matrix(long[][] a, long cutoff) {
            if (cutoff == 0)
                cutoff = Long.MAX_VALUE;
            for (int i = 0; i < a.length; i++) {
                if (i < cutoff) {
                    printMatrixRow(a[i], cutoff);
                } else {
                    out.println("     ...");
                    printMatrixRow(a[a.length - 1], cutoff);
                    break;
                }
            }
        }

        public void matrix(boolean[][] a, int cutoff) {
            if (cutoff == 0)
                cutoff = Integer.MAX_VALUE;
            for (int i = 0; i < a.length; i++) {
                if (i < cutoff) {
                    printMatrixRow(a[i], cutoff);
                } else {
                    out.println("     ...");
                    printMatrixRow(a[a.length - 1], cutoff);
                    break;
                }
            }
        }

        private void printMatrixRow(int[] a, int cutoff) {
            for (int j = 0; j < a.length; j++) {
                if (j < cutoff) {
                    out.printf("%6d  ", a[j]);
                } else {
                    out.printf(" ... %6d", a[a.length - 1]);
                    break;
                }
            }
            out.println();
        }

        private void printMatrixRow(long[] a, long cutoff) {
            for (int j = 0; j < a.length; j++) {
                if (j < cutoff) {
                    out.printf("%6d  ", a[j]);
                } else {
                    out.printf(" ... %6d", a[a.length - 1]);
                    break;
                }
            }
            out.println();
        }

        private void printMatrixRow(boolean[] a, int cutoff) {
            for (int j = 0; j < a.length; j++) {
                if (j < cutoff) {
                    out.print(a[j] ? "T " : "F ");
                } else {
                    out.print(" ... " + (a[a.length - 1] ? "T" : "F"));
                    break;
                }
            }
            out.println();
        }

    }

    static int dfs(int t) {
        if (a[t] != 0)
            return 0;
        a[t] = 1;
        int x = 0;
        for (Pair<Integer, Integer> i : e.get(t))
            if (a[i.first] == 0) {
                int y = dfs(i.first);
                if (y != 0)
                    answerEdges.add(i.second);
                x ^= y;
            }
        if (d[t] == -1) return 0;
        return x ^ d[t];
    }

    static int[] a = new int[300005];
    static int[] d = new int[300005];
    static ArrayList<ArrayList<Pair<Integer, Integer>>> e;
    static HashSet<Integer> answerEdges = new HashSet<>();

    public static void main(String[] args) throws IOException {

        int n = in.nextInt();
        int m = in.nextInt();

        e = new ArrayList<>();

        for (int i = 0; i < n; i++) {
            d[i] = in.nextInt();
            e.add(new ArrayList<>());
            a[i] = 0;
        }

        for (int j = 0; j < m; j++) {
            int x = in.nextInt() - 1;
            int y = in.nextInt() - 1;

            e.get(x).add(new Pair<>(y, j));
            e.get(y).add(new Pair<>(x, j));
        }

        int res = 0;

        for (int i = 0; i < n; i++) {
            if (d[i] == -1)
                res |= dfs(i);
        }

        res |= dfs(0);

        if (res != 0)
            out.println(-1);
        else {
            out.println(answerEdges.size());
            for (int i : answerEdges)
                out.print((i + 1) + " ");
            out.println();
        }
        log.flush();
        in.close();
    }
}