#include<bits/stdc++.h>

using namespace std;

using int64 = long long;
// const int mod = 1e9 + 7;
const int mod = 998244353;

const int64 infll = (1LL << 62) - 1;
const int inf = (1 << 30) - 1;

struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
  }
} iosetup;


template< typename T1, typename T2 >
ostream &operator<<(ostream &os, const pair< T1, T2 > &p) {
  os << p.first << " " << p.second;
  return os;
}

template< typename T1, typename T2 >
istream &operator>>(istream &is, pair< T1, T2 > &p) {
  is >> p.first >> p.second;
  return is;
}

template< typename T >
ostream &operator<<(ostream &os, const vector< T > &v) {
  for(int i = 0; i < (int) v.size(); i++) {
    os << v[i] << (i + 1 != v.size() ? " " : "");
  }
  return os;
}

template< typename T >
istream &operator>>(istream &is, vector< T > &v) {
  for(T &in : v) is >> in;
  return is;
}

template< typename T1, typename T2 >
inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }

template< typename T1, typename T2 >
inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

template< typename T = int64 >
vector< T > make_v(size_t a) {
  return vector< T >(a);
}

template< typename T, typename... Ts >
auto make_v(size_t a, Ts... ts) {
  return vector< decltype(make_v< T >(ts...)) >(a, make_v< T >(ts...));
}

template< typename T, typename V >
typename enable_if< is_class< T >::value == 0 >::type fill_v(T &t, const V &v) {
  t = v;
}

template< typename T, typename V >
typename enable_if< is_class< T >::value != 0 >::type fill_v(T &t, const V &v) {
  for(auto &e : t) fill_v(e, v);
}

template< typename F >
struct FixPoint : F {
  FixPoint(F &&f) : F(forward< F >(f)) {}

  template< typename... Args >
  decltype(auto) operator()(Args &&... args) const {
    return F::operator()(*this, forward< Args >(args)...);
  }
};

template< typename F >
inline decltype(auto) MFP(F &&f) {
  return FixPoint< F >{forward< F >(f)};
}

template< typename T = int >
struct Edge {
  int from, to;
  T cost;
  int idx;

  Edge() = default;

  Edge(int from, int to, T cost = 1, int idx = -1) : from(from), to(to), cost(cost), idx(idx) {}

  operator int() const { return to; }
};

template< typename T = int >
struct Graph {
  vector< vector< Edge< T > > > g;
  int es;

  Graph() = default;

  explicit Graph(int n) : g(n), es(0) {}

  size_t size() const {
    return g.size();
  }

  void add_directed_edge(int from, int to, T cost = 1) {
    g[from].emplace_back(from, to, cost, es++);
  }

  void add_edge(int from, int to, T cost = 1) {
    g[from].emplace_back(from, to, cost, es);
    g[to].emplace_back(to, from, cost, es++);
  }

  void read(int M, int padding = -1, bool weighted = false, bool directed = false) {
    for(int i = 0; i < M; i++) {
      int a, b;
      cin >> a >> b;
      a += padding;
      b += padding;
      T c = T(1);
      if(weighted) cin >> c;
      if(directed) add_directed_edge(a, b, c);
      else add_edge(a, b, c);
    }
  }
};

template< typename T = int >
using Edges = vector< Edge< T > >;

/**
 * @brief Cycle Detection(閉路検出)
 * @docs docs/cycle-detection.md
 */
template< typename T = int >
struct CycleDetection : Graph< T > {
  using Graph< T >::Graph;
  using Graph< T >::g;

  vector< int > used;
  Edges< T > pre, cyrcle;

  bool dfs(int idx) {
    used[idx] = 1;
    for(auto &e : g[idx]) {
      if(used[e] == 0) {
        pre[e] = e;
        if(dfs(e)) return true;
      } else if(used[e] == 1) {
        int cur = idx;
        while(cur != e) {
          cyrcle.emplace_back(pre[cur]);
          cur = pre[cur].from;
        }
        cyrcle.emplace_back(e);
        return true;
      }
    }

    used[idx] = 2;
    return false;
  }

  Edges< T > build() {
    used.assign(g.size(), 0);
    pre.resize(g.size());
    for(int i = 0; i < (int) g.size(); i++) {
      if(used[i] == 0 && dfs(i)) {
        reverse(begin(cyrcle), end(cyrcle));
        return cyrcle;
      }
    }
    return {};
  }
};

int main() {
  int H, W, N;
  cin >> H >> W >> N;
  vector< int > Y(N), X(N);
  for(int i = 0; i < N; i++) {
    cin >> Y[i] >> X[i];
    --Y[i], --X[i];
  }

  vector< vector< int > > ys(H), xs(W);
  for(int i = 0; i < N; i++) {
    ys[Y[i]].emplace_back(i);
    xs[X[i]].emplace_back(i);
  }
  CycleDetection<> g(N * 8);
  for(int i = 0; i < N; i++) {
    g.add_directed_edge(i, i + N);
    g.add_directed_edge(i + N + N, i + N + N + N);
  }
  int N4 = N + N + N + N;
  int N5 = N4 + N;
  int N6 = N5 + N;
  int N7 = N6 + N;
  for(int i = 0; i < W; i++) {
    for(int j = 1; j < xs[i].size(); j++) {
      g.add_directed_edge(xs[i][j - 1] + N4, xs[i][j] + N4);
      g.add_directed_edge(xs[i][j] + N5, xs[i][j - 1] + N5);
    }
    for(int j = 0; j < xs[i].size(); j++) {
      g.add_directed_edge(xs[i][j] + N4, xs[i][j] + N + N);
      g.add_directed_edge(xs[i][j] + N5, xs[i][j] + N + N);
      if(j > 0) {
        g.add_directed_edge(xs[i][j] + N, xs[i][j - 1] + N5);
      }
      if(j + 1 < xs[i].size()) {
        g.add_directed_edge(xs[i][j] + N, xs[i][j + 1] + N4);
      }
    }
  }
  for(int i = 0; i < H; i++) {
    for(int j = 1; j < ys[i].size(); j++) {
      g.add_directed_edge(ys[i][j - 1] + N6, ys[i][j] + N6);
      g.add_directed_edge(ys[i][j] + N7, ys[i][j - 1] + N7);
    }
    for(int j = 0; j < ys[i].size(); j++) {
      g.add_directed_edge(ys[i][j] + N6, ys[i][j]);
      g.add_directed_edge(ys[i][j] + N7, ys[i][j]);
      if(j > 0) {
        g.add_directed_edge(ys[i][j] + N + N + N, ys[i][j - 1] + N7);
      }
      if(j + 1 < ys[i].size()) {
        g.add_directed_edge(ys[i][j] + N + N + N, ys[i][j + 1] + N6);
      }
    }
  }
  g.build();
  vector< int > ret;
  for(auto &p : g.cyrcle) {
    if(0 <= p.from and p.from < N) {
      ret.emplace_back(p.from + 1);
    } else if(N + N <= p.from and p.from < N + N + N) {
      ret.emplace_back(p.from - N - N + 1);
    }
  }
  if(ret.empty()) {
    throw 0;
    cout << "-1\n";
  } else {
    assert(ret.size() >= 4);
    cout << ret.size() << "\n";
    cout << ret << "\n";
  }
}