#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; (i) < (int)(n); ++(i))
#define REP3(i, m, n) for (int i = (m); (i) < (int)(n); ++(i))
#define REP_R(i, n) for (int i = (int)(n)-1; (i) >= 0; --(i))
#define REP3R(i, m, n) for (int i = (int)(n)-1; (i) >= (int)(m); --(i))
#define ALL(x) ::std::begin(x), ::std::end(x)
using namespace std;

std::vector<int> solve(int h, int w, int n, const std::vector<int> &x, const std::vector<int> &y) {
    vector<vector<int>> row(h);
    vector<vector<int>> col(w);
    REP (i, n) {
        row[y[i]].push_back(i);
        col[x[i]].push_back(i);
    }

    vector<bool> used(n);
    vector<int> ans;
    auto go = [&](auto &&go, int i, int parent) -> bool {
        if (used[i]) {
            auto it = find(ALL(ans), i);
            if (it != ans.end() and (ans.end() - it) % 2 == 0) {
                int k = it - ans.begin();
                ans.erase(ans.begin(), it);
                if (k % 2 == 1) {
                    rotate(ans.begin(), ans.begin() + 1, ans.end());
                }
                return true;
            }
            return false;
        }
        ans.push_back(i);
        used[i] = true;
        if (ans.size() % 2 == 0) {
            for (int j : row[y[i]]) {
                if (j != i and j != parent) {
                    if (go(go, j, i)) {
                        return true;
                    }
                }
            }
        } else {
            for (int j : col[x[i]]) {
                if (j != i and j != parent) {
                    if (go(go, j, i)) {
                        return true;
                    }
                }
            }
        }
        ans.pop_back();
        return false;
    };
    REP (i, n) {
        if (not used[i]) {
            if (go(go, i, -1)) {
                return ans;
            }
        }
    }
    return ans;
}

// generated by oj-template v4.8.0 (https://github.com/online-judge-tools/template-generator)
int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    int H, W;
    int N;
    std::cin >> H >> W >> N;
    std::vector<int> x(N), y(N);
    REP (i, N) { std::cin >> y[i] >> x[i]; -- x[i]; -- y[i]; }
    vector<int> ans = solve(H, W, N, x, y);
    if (ans.empty()) {
        std::cout << -1 << '\n';
    } else {
        std::cout << (int)ans.size() << '\n';
        REP (i, (int)ans.size()) { std::cout << ans[i] + 1 << ' '; }
        std::cout << '\n';
    }
    return 0;
}