#include using namespace std; using ll = long long; using ld = long double; template using V = vector; using VI = V; using VL = V; using VS = V; template using PQ = priority_queue, greater>; using graph = V; template using w_graph = V>>; #define FOR(i,a,n) for(int i=(a);i<(n);++i) #define eFOR(i,a,n) for(int i=(a);i<=(n);++i) #define rFOR(i,a,n) for(int i=(n)-1;i>=(a);--i) #define erFOR(i,a,n) for(int i=(n);i>=(a);--i) #define all(a) a.begin(),a.end() #define rall(a) a.rbegin(),a.rend() #define out(y,x) ((y)<0||h<=(y)||(x)<0||w<=(x)) #ifdef _DEBUG #define line cout << "-----------------------------\n" #define stop system("pause") #endif constexpr ll INF = 1000000000; constexpr ll LLINF = 1LL << 61; constexpr ll mod = 1000000007; constexpr ll MOD = 998244353; constexpr ld eps = 1e-10; templateinline bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; }return false; } templateinline bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; }return false; } inline void init() { cin.tie(nullptr); cout.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); } templateinline istream& operator>>(istream& is, V& v) { for (auto& a : v)is >> a; return is; } templateinline istream& operator>>(istream& is, pair& p) { is >> p.first >> p.second; return is; } templateinline V vec(size_t a) { return V(a); } templateinline V defvec(T def, size_t a) { return V(a, def); } templateinline auto vec(size_t a, Ts... ts) { return V(ts...))>(a, vec(ts...)); } templateinline auto defvec(T def, size_t a, Ts... ts) { return V(def, ts...))>(a, defvec(def, ts...)); } templateinline void print(const T& a) { cout << a << "\n"; } templateinline void print(const T& a, const Ts&... ts) { cout << a << " "; print(ts...); } templateinline void print(const V& v) { for (int i = 0; i < v.size(); ++i)cout << v[i] << (i == v.size() - 1 ? "\n" : " "); } templateinline void print(const V>& v) { for (auto& a : v)print(a); } templateinline T sum(const V& a, int l, int r) { return 0 <= l && l <= r && r < a.size() ? a[r] - (l == 0 ? 0 : a[l - 1]) : 0; } templateinline void END(T s) { print(s); exit(0); } void END() { exit(0); } template class Indexer { static_assert(M > 0, "M must be positive"); array lim; int siz; public: Indexer(initializer_list lim_init) { assert(lim_init.size() == M); copy(all(lim_init), lim.begin()); siz = 1; FOR(i, 0, M) { assert(lim[i] > 0); siz *= lim[i]; } }; int operator() (initializer_list target_init) { assert(target_init.size() == M); array target; copy(all(target_init), target.begin()); int res = 0; FOR(i, 0, M)res = res * lim[i] + target[i]; return res; } array operator() (int a) { assert(a < size()); array res; rFOR(i, 0, M) { res[i] = a % lim[i]; a /= lim[i]; } return res; } int size() { return siz; } }; int main() { init(); int h, w, n; cin >> h >> w >> n; VI x(n), y(n); V>> gyo(h), ret(w); FOR(i, 0, n) { cin >> x[i] >> y[i]; --x[i], --y[i]; gyo[y[i]].emplace_back(x[i], i); ret[x[i]].emplace_back(y[i], i); } Indexer<2> indexer({ 2,n }); graph g(indexer.size()); FOR(i, 0, n) { g[indexer({ 0,i })].push_back(indexer({ 1,i })); g[indexer({ 1,i })].push_back(indexer({ 0,i })); } FOR(i, 0, h) { sort(all(gyo[i])); FOR(j, 1, gyo[i].size()) { g[indexer({ 0,gyo[i][j - 1].second })].push_back(indexer({ 0,gyo[i][j].second })); g[indexer({ 0,gyo[i][j].second })].push_back(indexer({ 0,gyo[i][j - 1].second })); } } FOR(i, 0, w) { sort(all(ret[i])); FOR(j, 1, ret[i].size()) { g[indexer({ 1,ret[i][j - 1].second })].push_back(indexer({ 1,ret[i][j].second })); g[indexer({ 1,ret[i][j].second })].push_back(indexer({ 1,ret[i][j - 1].second })); } } VI seen(g.size()); deque ans; int root = -1; auto dfs = [&](auto&& f, int cur, int par)->bool { seen[cur] = 1; for (int to : g[cur]) { if (to == par || seen[to] == 2)continue; if (seen[to] == 0) { if (f(f, to, cur)) { if (indexer(cur)[1] == indexer(to)[1]) { ans.push_back(indexer(cur)[1]); } if (root == cur) { if (y[ans[0]] != y[ans[1]]) { ans.push_back(ans.front()); ans.pop_front(); } print(ans.size()); FOR(i, 0, ans.size()) { if (i)cout << " "; cout << ans[i] + 1; } cout << "\n"; exit(0); } else { return true; } } } else if (seen[to] == 1) { root = to; if (indexer(cur)[1] == indexer(to)[1]) { ans.push_back(indexer(cur)[1]); } return true; } } seen[cur] = 2; return false; }; FOR(i, 0, g.size())if (seen[i] == 0)dfs(dfs, i, -1); print(-1); return 0; }