import sys

sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
# inf = 10**16
md = 998244353
# md = 10**9+7

h, w, n = LI()
to = [[] for _ in range(h+w)]

xytoi = {}
for i in range(n):
    x, y = LI1()
    y += h
    to[x].append(y)
    to[y].append(x)
    xytoi[x, y] = i

vis = [0]*(h+w)
def dfs(u):
    stack = [(u, -1, True)]
    res = []
    while stack:
        u, par, first = stack.pop()
        if first:
            vis[u] = 1
            stack.append((u, par, False))
            for v in to[u]:
                if v == par: continue
                if vis[v] == 2: continue
                if vis[v] == 1:
                    res = [v, u, par]
                    break
                stack.append((v, u, True))
        else:
            if res and res[-1] == u:
                res.append(par)
            if res and res[0] == res[-1]: return res
            vis[u] = 2

ans = []
for u in range(h):
    if vis[u]: continue
    uu = dfs(u)
    if uu:
        for u0, u1 in zip(uu, uu[1:]):
            if u0 > u1: u0, u1 = u1, u0
            i = xytoi[u0, u1]
            ans.append(i+1)
        if uu[0] > uu[1]:
            ans = [ans[-1]]+ans[:-1]
        break

if ans:
    print(len(ans))
    print(*ans)
else:
    print(-1)