import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.List;

public class Main {
	static int h, w, n, hw;
	static List<List<Hen>> list;

	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] sa = br.readLine().split(" ");
		h = Integer.parseInt(sa[0]);
		w = Integer.parseInt(sa[1]);
		n = Integer.parseInt(sa[2]);
		hw = h + w;
		list = new ArrayList<>(hw);
		for (int i = 0; i < hw; i++) {
			list.add(new ArrayList<>());
		}
		Hen[] arr = new Hen[n];
		for (int i = 0; i < n; i++) {
			sa = br.readLine().split(" ");
			Hen o = new Hen();
			o.i = i;
			o.x = Integer.parseInt(sa[0]) - 1;
			o.y = Integer.parseInt(sa[1]) - 1 + h;
			list.get(o.x).add(o);
			list.get(o.y).add(o);
			arr[i] = o;
		}
		br.close();

		for (Hen o : arr) {
			if (!o.used) {
				if (dfs(o.x, null, new LinkedHashSet<>())) {
					return;
				}
			}
		}
		System.out.println(-1);
	}

	static boolean dfs(int x, Hen p, LinkedHashSet<Hen> his) {
		for (Hen o : list.get(x)) {
			o.used = true;
			if (o != p) {
				if (his.contains(o)) {
					Hen[] arr = his.toArray(new Hen[0]);
					int s = 0;
					for (int i = 0; i < arr.length; i++) {
						if (arr[i] == o) {
							s = i;
							break;
						}
					}
					System.out.println(arr.length - s);
					StringBuilder sb = new StringBuilder();
					for (int i = s; i < arr.length; i++) {
						sb.append(arr[i].i + 1).append(' ');
					}
					sb.deleteCharAt(sb.length() - 1);
					System.out.println(sb.toString());
					return true;
				}
				his.add(o);
				int nx = o.x;
				if (nx == x) {
					nx = o.y;
				}
				if (dfs(nx, o, his)) {
					return true;
				}
				his.remove(o);
			}
		}
		return false;
	}

	static class Hen {
		int x, y, i;
		boolean used;
	}
}