#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
constexpr int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
constexpr int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

template <typename CostType>
struct Edge {
  int src, dst; CostType cost;
  Edge(int src, int dst, CostType cost = 0) : src(src), dst(dst), cost(cost) {}
  inline bool operator<(const Edge &x) const {
    return cost != x.cost ? cost < x.cost : dst != x.dst ? dst < x.dst : src < x.src;
  }
  inline bool operator<=(const Edge &x) const { return !(x < *this); }
  inline bool operator>(const Edge &x) const { return x < *this; }
  inline bool operator>=(const Edge &x) const { return !(*this < x); }
};

int main() {
  int h, w, n; cin >> h >> w >> n;
  vector<int> x(n), y(n); REP(i, n) cin >> x[i] >> y[i], --x[i], --y[i];
  vector<vector<Edge<int>>> graph(h + w);
  REP(i, n) {
    graph[x[i]].emplace_back(x[i], y[i] + h, i);
    graph[y[i] + h].emplace_back(y[i] + h, x[i], i);
  }
  vector<int> visited(h + w, false);
  vector<Edge<int>> ans;
  auto f = [&](auto &&f, int ver) -> void {
    if (visited[ver]) {
      vector<int> t;
      while (ans.back().src != ver) {
        t.emplace_back(ans.back().cost);
        ans.pop_back();
      }
      t.emplace_back(ans.back().cost);
      reverse(ALL(t));
      if (x[t[0]] == x[t[1]]) rotate(t.begin(), t.begin() + 1, t.end());
      const int X = t.size();
      assert(X >= 4 && X % 2 == 0);
      cout << X << '\n';
      REP(i, X) {
        if (i & 1) {
          assert(x[t[i]] == x[t[(i + 1) % X]]);
        } else {
          assert(y[t[i]] == y[t[(i + 1) % X]]);
        }
        cout << t[i] + 1 << " \n"[i + 1 == X];
      }
      exit(0);
    }
    visited[ver] = true;
    for (const Edge<int> &e : graph[ver]) {
      if (ans.empty() || e.cost != ans.back().cost) {
        ans.emplace_back(e);
        f(f, e.dst);
        ans.pop_back();
      }
    }
  };
  REP(i, h) {
    if (!visited[i]) f(f, i);
  }
  cout << "-1\n";
  return 0;
}