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():
    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])
    def dfs(points,edges):
        if len(edges)==4:
            print(4)
            print(*edges)
            exit()
        for v,num in graph[points[-1]]:
            if num not in edges:
                dfs(points+[v],edges+[num])
    for i in range(h):
        dfs([i],[])
    print(-1)
    


if __name__ == '__main__':
    main()