import sys
from collections import defaultdict, Counter, deque
from itertools import permutations, combinations, product, combinations_with_replacement, groupby, accumulate
import operator
from math import sqrt, gcd, factorial
# from math import isqrt, prod, comb  #python3.8用(notpypy)
#from bisect import bisect_left, bisect_right
#from functools import lru_cache, reduce
#from heapq import heappush, heappop, heapify, heappushpop, heapreplace
#import numpy as np
#import networkx as nx
#from networkx.utils import UnionFind
#from numba import njit, b1, i1, i4, i8, f8
# numba例 @njit(i1(i4[:], i8[:, :]),cache=True) 引数i4配列、i8 2次元配列,戻り値i1
#from scipy.sparse import csr_matrix
#from scipy.sparse.csgraph import shortest_path, floyd_warshall, dijkstra, bellman_ford, johnson, NegativeCycleError, maximum_bipartite_matching, maximum_flow, minimum_spanning_tree
def input(): return sys.stdin.readline().rstrip()
def divceil(n, k): return 1+(n-1)//k  # n/kの切り上げを返す
def yn(hantei, yes='Yes', no='No'): print(yes if hantei else no)


def main():
    sys.setrecursionlimit(10**5+1)
    mod = 10**9+7
    mod2 = 998244353
    h, w, n = map(int, input().split())
    xy = [list(map(lambda x: int(x)-1, input().split())) for i in range(n)]
    graph = [[] for i in range(h+w)]
    for i, (x, y) in enumerate(xy):
        graph[x].append([y+h, i+1])
        graph[y+h].append([x, i+1])
    visited = [0]*(h+w)
    points = []
    edges = []

    def dfs(u, p):
        visited[u] = 1
        for v, num in graph[u]:
            if v != p:
                if visited[v]==1 and v < h:
                    #print(points)
                    #print(edges)
                    ans=edges[points.index(v)+1:]+[num]
                    print(len(ans))
                    print(*ans)
                    #print(points)
                    #for aa in ans:
                    #    print(xy[aa-1][0],xy[aa-1][1]+h)
                    exit()
                if visited[v]==1 and v >= h:
                    continue
                points.append(v)
                edges.append(num)
                dfs(v, u)
        points.pop()
        edges.pop()

    for i in range(h):
        if visited[i]==0:
            points=[i]
            edges=[-1]
            #print(i)
            dfs(i, -1)
    print(-1)


if __name__ == '__main__':
    main()