#include #define REP_(i, a_, b_, a, b, ...) \ for (int i = (a), END_##i = (b); i < END_##i; ++i) #define REP(i, ...) REP_(i, __VA_ARGS__, __VA_ARGS__, 0, __VA_ARGS__) #define ALL(x) std::begin(x), std::end(x) using i64 = long long; template inline bool chmax(T &a, U b) { return a < b and ((a = std::move(b)), true); } template inline bool chmin(T &a, U b) { return a > b and ((a = std::move(b)), true); } template inline int ssize(const T &a) { return (int) std::size(a); } template std::istream &operator>>(std::istream &is, std::vector &a) { for (auto &x : a) is >> x; return is; } template std::ostream &operator<<(std::ostream &os, const std::pair &a) { return os << "(" << a.first << ", " << a.second << ")"; } template std::ostream &print_seq(const Container &a, std::string_view sep = " ", std::string_view ends = "\n", std::ostream &os = std::cout) { auto b = std::begin(a), e = std::end(a); for (auto it = std::begin(a); it != e; ++it) { if (it != b) os << sep; os << *it; } return os << ends; } template struct is_iterable : std::false_type {}; template struct is_iterable())), decltype(std::end(std::declval()))>> : std::true_type { }; template::value && !std::is_same::value && !std::is_same::value>> std::ostream &operator<<(std::ostream &os, const T &a) { return print_seq(a, ", ", "", (os << "{")) << "}"; } void print() { std::cout << "\n"; } template void print(const T &x) { std::cout << x << "\n"; } template void print(const Head &head, Tail... tail) { std::cout << head << " "; print(tail...); } void read_from_cin() {} template void read_from_cin(T &value, Ts &...args) { std::cin >> value; read_from_cin(args...); } #define INPUT(type, ...) \ type __VA_ARGS__; \ read_from_cin(__VA_ARGS__) #ifdef MY_DEBUG #include "debug_dump.hpp" #else #define DUMP(...) #endif using namespace std; auto solve() -> optional> { INPUT(i64, H, W, n); vector> spots(n); vector> rows(H), cols(W); REP(i, n) { INPUT(int, x, y); --x, --y; spots[i] = {x, y}; rows[x].push_back(i); cols[y].push_back(i); } vector par(n, -1), done(n, false), depth(n, -1); auto dfs = [&](auto &dfs, int v, int d) -> optional> { int x, y; tie(x, y) = spots[v]; vector &nexts = (d & 1) ? rows[x] : cols[y]; for (int u : nexts) { if (done[u]) { if (depth[v] - depth[u] < 3) continue; if ((depth[v] & 1) == (depth[u] & 1)) continue; vector path; for (int w = v; w != -1; w = par[w]) { path.push_back(w); } reverse(ALL(path)); if (depth[u] & 1) { std::rotate(path.begin(), path.begin() + 1, path.end()); } return path; } done[u] = true; depth[u] = depth[v] + 1; par[u] = v; auto sub = dfs(dfs, u, d + 1); if (sub) return sub; } return nullopt; }; REP(iter, 2) { done.assign(n, false); depth.assign(n, -1); par.assign(n, -1); REP(v, n) { if (done[v]) continue; done[v] = true; depth[v] = 0; auto sub = dfs(dfs, v, iter); if (sub) return sub; } } return nullopt; } int main() { ios_base::sync_with_stdio(false), cin.tie(nullptr); cout << std::fixed << std::setprecision(15); int t = 1; REP(test_case, t) { auto ans = solve(); if (not ans) { print(-1); } else { auto &v = ans.value(); print(v.size()); for (auto &x : v) ++x; print_seq(v); } } }