import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**7)
from collections import *

H, W, N = map(int, input().split())
G = [[] for i in range(H + W)]
D = dict()
for i in range(N):
    x, y = map(int, input().split())
    x, y = x - 1, y - 1
    if i == 0:
        s, g = x, y + H
    G[x].append(y + H)
    G[y + H].append(x)
    D[(x, y+H)] = i + 1
    D[(y+H, x)] = i + 1

seen = [0] * (H + W)
seen2 = [0] * (H + W)
temp = []

def dfs(s, p):
    for u in G[s]:
        if u == p:
            continue
        if seen[u]:
            if seen2[u] == 0:
                ans = []
                now = u
                while temp:
                    ans.append(D[(now, temp[-1])])
                    now = temp.pop()
                ans.reverse()
                print(len(ans))
                print(*ans)
                exit()
            continue
            
        seen[u] = 1
        seen2[u] = 1
        temp.append(u)
        dfs(u, s)
        seen2[u] = 0
        temp.pop()
    return 


for i in range(H):
    if seen[i]:
        continue
    temp = [i]
    seen[i] = 1
    dfs(i, -1)

print(-1)