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.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.stream.IntStream;
import java.util.Arrays;
import java.io.IOException;
import java.io.Reader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import java.io.BufferedReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        MyInput in = new MyInput(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB {
        public void solve(int testNumber, MyInput in, PrintWriter out) {
            int n = in.nextInt();
            int m = in.nextInt();
            int[] d = in.nextIntArray(n);
            int[][] es = in.nextIntArray2D(m, 2);

            Graph graph = Graph.fromEdges(n, es);
            Tree tree = graph.dfsTree(0);

            int remain = Arrays.stream(d).filter(value -> value == 1).sum() % 2;
            for (int i = 0; i < d.length; i++) {
                if (d[i] == -1 && remain == 1) {
                    d[i] = 1;
                    remain = 0;
                }
                if (d[i] == -1) {
                    d[i] = 0;
                }
            }
            if (remain == 1) {
                out.println(-1);
                return;
            }

            List<Integer> edgeIds = new ArrayList<>();
            for (int v : tree.inversedDfsOrder()) {
                for (Edge e : tree.edges(v)) {
                    if (d[e.to] == 1) {
                        edgeIds.add(e.edgeId);
                        d[v] ^= 1;
                    }
                }
            }

            out.println(edgeIds.size());
            for (int e : edgeIds) out.println(e + 1);
        }

    }

    static class MyInput {
        private final BufferedReader in;
        private static int pos;
        private static int readLen;
        private static final char[] buffer = new char[1024 * 8];
        private static char[] str = new char[500 * 8 * 2];
        private static boolean[] isDigit = new boolean[256];
        private static boolean[] isSpace = new boolean[256];
        private static boolean[] isLineSep = new boolean[256];

        static {
            for (int i = 0; i < 10; i++) {
                isDigit['0' + i] = true;
            }
            isDigit['-'] = true;
            isSpace[' '] = isSpace['\r'] = isSpace['\n'] = isSpace['\t'] = true;
            isLineSep['\r'] = isLineSep['\n'] = true;
        }

        public MyInput(InputStream is) {
            in = new BufferedReader(new InputStreamReader(is));
        }

        public int read() {
            if (pos >= readLen) {
                pos = 0;
                try {
                    readLen = in.read(buffer);
                } catch (IOException e) {
                    throw new RuntimeException();
                }
                if (readLen <= 0) {
                    throw new MyInput.EndOfFileRuntimeException();
                }
            }
            return buffer[pos++];
        }

        public int nextInt() {
            int len = 0;
            str[len++] = nextChar();
            len = reads(len, isSpace);
            int i = 0;
            int ret = 0;
            if (str[0] == '-') {
                i = 1;
            }
            for (; i < len; i++) ret = ret * 10 + str[i] - '0';
            if (str[0] == '-') {
                ret = -ret;
            }
            return ret;
        }

        public char nextChar() {
            while (true) {
                final int c = read();
                if (!isSpace[c]) {
                    return (char) c;
                }
            }
        }

        int reads(int len, boolean[] accept) {
            try {
                while (true) {
                    final int c = read();
                    if (accept[c]) {
                        break;
                    }
                    if (str.length == len) {
                        char[] rep = new char[str.length * 3 / 2];
                        System.arraycopy(str, 0, rep, 0, str.length);
                        str = rep;
                    }
                    str[len++] = (char) c;
                }
            } catch (MyInput.EndOfFileRuntimeException e) {
            }
            return len;
        }

        public int[] nextIntArray(final int n) {
            final int[] res = new int[n];
            for (int i = 0; i < n; i++) {
                res[i] = nextInt();
            }
            return res;
        }

        public int[][] nextIntArray2D(final int n, final int k) {
            final int[][] res = new int[n][];
            for (int i = 0; i < n; i++) {
                res[i] = nextIntArray(k);
            }
            return res;
        }

        static class EndOfFileRuntimeException extends RuntimeException {
        }

    }

    static class ArrayAlgorithms {
        public static int[] reverse(int[] ary) {
            int V = ary.length;
            for (int i = 0; i < V / 2; i++) {
                int t = ary[i];
                ary[i] = ary[V - 1 - i];
                ary[V - 1 - i] = t;
            }
            return ary;
        }

    }

    static class Edge {
        public final int edgeId;
        public final int to;

        public Edge(int to, int edgeId) {
            this.to = to;
            this.edgeId = edgeId;
        }


        public String toString() {
            return String.format("[Edge id=%d, to=%d]", edgeId, to);
        }

    }

    static class Graph {
        int V;
        Vertex[] vertex;

        public Graph(int V) {
            this.V = V;
            vertex = new Vertex[V];
            for (int i = 0; i < V; i++) vertex[i] = new Vertex();
        }

        public static Graph fromEdges(int n, int[][] edges) {
            Graph g = new Graph(n);
            for (int i = 0; i < edges.length; i++) {
                int s = edges[i][0] - 1, t = edges[i][1] - 1;
                g.addEdge(s, t, i);
            }
            return g;
        }

        public void addEdge(int s, int t, int edgeId) {
            vertex[s].addEdge(new Edge(t, edgeId));
            vertex[t].addEdge(new Edge(s, edgeId));
        }

        public Tree dfsTree(int r) {
            Tree tree = new Tree(V, r);

            int[] st = new int[V];
            int sp = 0;
            int len = 0;
            boolean[] vis = new boolean[V];

            vis[r] = true;
            st[sp++] = r;
            while (sp > 0) {
                int v = st[--sp];
                for (Edge e : vertex[v].edges)
                    if (!vis[e.to]) {
                        vis[e.to] = true;
                        st[sp++] = e.to;
                        tree.addEdge(v, e);
                    }
            }
            return tree;
        }

    }

    static class Vertex {
        public final List<Edge> edges = new ArrayList<>();

        public void addEdge(Edge e) {
            edges.add(e);
        }

    }

    static class Tree {
        int V;
        int root;
        Vertex[] vertex;

        public Tree(int V, int root) {
            this.V = V;
            this.root = root;
            vertex = new Vertex[V];
            for (int i = 0; i < V; i++) vertex[i] = new Vertex();
        }

        public void addEdge(int s, Edge e) {
            vertex[s].addEdge(e);
        }

        public List<Edge> edges(int v) {
            return vertex[v].edges;
        }

        public int[] dfsOrder() {
            int[] st = new int[V];
            int sp = 0, len = 0;
            int[] order = new int[V];
            boolean[] vis = new boolean[V];

            vis[root] = true;
            st[sp++] = root;
            while (sp > 0) {
                int v = st[--sp];
                order[len++] = v;
                for (Edge e : vertex[v].edges)
                    if (!vis[e.to]) {
                        vis[e.to] = true;
                        st[sp++] = e.to;
                    }
            }
            return order;
        }

        public int[] inversedDfsOrder() {
            return ArrayAlgorithms.reverse(dfsOrder());
        }

    }
}