#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <complex>
#include <deque>
#include <forward_list>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
using lint = long long;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(nullptr), ios::sync_with_stdio(false), cout << fixed << setprecision(20); }; } fast_ios_;
#define ALL(x) (x).begin(), (x).end()
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template <typename T, typename V>
void ndarray(vector<T>& vec, const V& val, int len) { vec.assign(len, val); }
template <typename T, typename V, typename... Args> void ndarray(vector<T>& vec, const V& val, int len, Args... args) { vec.resize(len), for_each(begin(vec), end(vec), [&](T& v) { ndarray(v, val, args...); }); }
template <typename T> bool chmax(T &m, const T q) { return m < q ? (m = q, true) : false; }
template <typename T> bool chmin(T &m, const T q) { return m > q ? (m = q, true) : false; }
int floor_lg(long long x) { return x <= 0 ? -1 : 63 - __builtin_clzll(x); }
template <typename T1, typename T2> pair<T1, T2> operator+(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }
template <typename T1, typename T2> pair<T1, T2> operator-(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }
template <typename T> vector<T> sort_unique(vector<T> vec) { sort(vec.begin(), vec.end()), vec.erase(unique(vec.begin(), vec.end()), vec.end()); return vec; }
template <typename T> int arglb(const std::vector<T> &v, const T &x) { return std::distance(v.begin(), std::lower_bound(v.begin(), v.end(), x)); }
template <typename T> int argub(const std::vector<T> &v, const T &x) { return std::distance(v.begin(), std::upper_bound(v.begin(), v.end(), x)); }
template <typename T> istream &operator>>(istream &is, vector<T> &vec) { for (auto &v : vec) is >> v; return is; }
template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) { os << '['; for (auto v : vec) os << v << ','; os << ']'; return os; }
template <typename T, size_t sz> ostream &operator<<(ostream &os, const array<T, sz> &arr) { os << '['; for (auto v : arr) os << v << ','; os << ']'; return os; }
#if __cplusplus >= 201703L
template <typename... T> istream &operator>>(istream &is, tuple<T...> &tpl) { std::apply([&is](auto &&... args) { ((is >> args), ...);}, tpl); return is; }
template <typename... T> ostream &operator<<(ostream &os, const tuple<T...> &tpl) { os << '('; std::apply([&os](auto &&... args) { ((os << args << ','), ...);}, tpl); return os << ')'; }
#endif
template <typename T> ostream &operator<<(ostream &os, const deque<T> &vec) { os << "deq["; for (auto v : vec) os << v << ','; os << ']'; return os; }
template <typename T> ostream &operator<<(ostream &os, const set<T> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <typename T, typename TH> ostream &operator<<(ostream &os, const unordered_set<T, TH> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <typename T> ostream &operator<<(ostream &os, const multiset<T> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &pa) { os << '(' << pa.first << ',' << pa.second << ')'; return os; }
template <typename TK, typename TV> ostream &operator<<(ostream &os, const map<TK, TV> &mp) { os << '{'; for (auto v : mp) os << v.first << "=>" << v.second << ','; os << '}'; return os; }
template <typename TK, typename TV, typename TH> ostream &operator<<(ostream &os, const unordered_map<TK, TV, TH> &mp) { os << '{'; for (auto v : mp) os << v.first << "=>" << v.second << ','; os << '}'; return os; }
#ifdef HITONANODE_LOCAL
const string COLOR_RESET = "\033[0m", BRIGHT_GREEN = "\033[1;32m", BRIGHT_RED = "\033[1;31m", BRIGHT_CYAN = "\033[1;36m", NORMAL_CROSSED = "\033[0;9;37m", RED_BACKGROUND = "\033[1;41m", NORMAL_FAINT = "\033[0;2m";
#define dbg(x) cerr << BRIGHT_CYAN << #x << COLOR_RESET << " = " << (x) << NORMAL_FAINT << " (L" << __LINE__ << ") " << __FILE__ << COLOR_RESET << endl
#define dbgif(cond, x) ((cond) ? cerr << BRIGHT_CYAN << #x << COLOR_RESET << " = " << (x) << NORMAL_FAINT << " (L" << __LINE__ << ") " << __FILE__ << COLOR_RESET << endl : cerr)
#else
#define dbg(x) (x)
#define dbgif(cond, x) 0
#endif

// Shortest cycle detection of UNDIRECTED SIMPLE graphs based on 01-BFS
// Assumption: only two types of edges are permitted: weight = 0 or W ( > 0)
// Complexity: O(E)
// Verified: <https://codeforces.com/contest/1325/problem/E>
struct ShortestCycle01 {
    const int INF = std::numeric_limits<int>::max() / 2;
    int V, E;
    int INVALID = -1;
    std::vector<std::vector<std::pair<int, int>>> to; // (nxt, weight)
    ShortestCycle01() = default;
    ShortestCycle01(int V) : V(V), E(0), to(V) {}
    void add_edge(int s, int t, int len) {
        assert(0 <= s and s < V);
        assert(0 <= t and t < V);
        assert(len >= 0);
        to[s].emplace_back(t, len);
        to[t].emplace_back(s, len);
        E++;
    }

    std::vector<int> dist;
    std::vector<int> prev;
    // Find minimum length simple cycle which passes vertex `v`
    // - return: (LEN, (a, b))
    //   - LEN: length of the shortest cycles if exists, INF otherwise.
    //   - the cycle consists of vertices [v, ..., prev[prev[a]], prev[a], a, b, prev[b], prev[prev[b]], ..., v]
    std::pair<int, std::pair<int, int>> Solve(int v) {
        assert(0 <= v and v < V);
        dist.assign(V, INF);
        dist[v] = 0;
        prev.assign(V, -1);
        std::deque<std::pair<int, int>> bfsq;
        std::vector<std::pair<std::pair<int, int>, int>> add_edge;
        bfsq.emplace_back(v, -1);
        while (!bfsq.empty()) {
            int now = bfsq.front().first, prv = bfsq.front().second;
            bfsq.pop_front();
            for (auto nxt : to[now])
                if (nxt.first != prv) {
                    if (dist[nxt.first] == INF) {
                        dist[nxt.first] = dist[now] + nxt.second;
                        prev[nxt.first] = now;
                        if (nxt.second)
                            bfsq.emplace_back(nxt.first, now);
                        else
                            bfsq.emplace_front(nxt.first, now);
                    } else
                        add_edge.emplace_back(std::make_pair(now, nxt.first), nxt.second);
                }
        }
        int minimum_cycle = INF;
        int s = -1, t = -1;
        for (auto edge : add_edge) {
            int a = edge.first.first, b = edge.first.second;
            int L = dist[a] + dist[b] + edge.second;
            if (L < minimum_cycle) minimum_cycle = L, s = a, t = b;
        }
        return std::make_pair(minimum_cycle, std::make_pair(s, t));
    }
};

// UnionFind Tree (0-indexed), based on size of each disjoint set
struct UnionFind {
    std::vector<int> par, cou;
    UnionFind(int N = 0) : par(N), cou(N, 1) { iota(par.begin(), par.end(), 0); }
    int find(int x) { return (par[x] == x) ? x : (par[x] = find(par[x])); }
    bool unite(int x, int y) {
        x = find(x), y = find(y);
        if (x == y) return false;
        if (cou[x] < cou[y]) std::swap(x, y);
        par[y] = x, cou[x] += cou[y];
        return true;
    }
    int count(int x) { return cou[find(x)]; }
    bool same(int x, int y) { return find(x) == find(y); }
};


int main() {
    int H, W, N;
    cin >> H >> W >> N;
    const int X = 100001;
    ShortestCycle01 graph(X * 2);
    UnionFind uf(X * 2);
    int xi = -1;
    map<pint, int> mp;
    REP(i, N) {
        int x, y;
        cin >> x >> y;
        graph.add_edge(x, y + X, 1);
        if (!uf.unite(x, y + X)) {
            xi = x;
        }
        mp[pint(x, y + X)] = i + 1;
    }
    if (xi < 0) {
        puts("-1");
        return 0;
    }
    auto [len, p] = graph.Solve(xi);
    auto [a, b] = p;
    vector<int> q;
    int h = a;
    while (h != xi) {
        q.push_back(h);
        h = graph.prev[h];
    }
    q.push_back(h);
    reverse(ALL(q));
    h = b;
    while (h != xi) {
        q.push_back(h);
        h = graph.prev[h];
    }
    cout << q.size() << '\n';
    REP(i, q.size()) {
        int a = q[i], b = q[(i + 1) % q.size()];
        if (a > b) swap(a, b);
        cout << mp[pint(a, b)] << ' ';
    }
    cout << '\n';
}