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 n, n2;
	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(" ");
		n = Integer.parseInt(sa[2]);
		n2 = n * 2;
		list = new ArrayList<>(n2);
		for (int i = 0; i < n2; i++) {
			list.add(new ArrayList<>());
		}
		for (int i = 0; i < n; i++) {
			sa = br.readLine().split(" ");
			Hen h = new Hen();
			h.i = i;
			h.x = Integer.parseInt(sa[0]) - 1;
			h.y = Integer.parseInt(sa[1]) - 1 + n;
			list.get(h.x).add(h);
			list.get(h.y).add(h);
		}
		br.close();

		for (int i = 0; i < n2; i++) {
			if (dfs(i, null, new LinkedHashSet<>())) {
				return;
			}
		}
		System.out.println(-1);
	}

	static boolean dfs(int x, Hen p, LinkedHashSet<Hen> his) {
		for (Hen h : list.get(x)) {
			if (h != p) {
				if (his.contains(h)) {
					System.out.println(his.size());
					StringBuilder sb = new StringBuilder();
					for (Hen h2 : his) {
						sb.append(h2.i % n + 1).append(' ');
					}
					sb.deleteCharAt(sb.length() - 1);
					System.out.println(sb.toString());
					return true;
				}
				his.add(h);
				int nx = h.x;
				if (nx == x) {
					nx = h.y;
				}
				if (dfs(nx, h, his)) {
					return true;
				}
				his.remove(h);
			}
		}
		return false;
	}

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