#include "bits/stdc++.h"
#include "atcoder/all"
using namespace std;
using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
//const bool debug = false;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
vector<int>to[200005];
bool use[200005];
bool b;
vector<int>ans;
void dfs(int v, int root, int p = -1) {
	use[v] = true;
	for (auto e : to[v]) {
		if (root == e) b = true;
		if (b)break;
		if (use[e])continue;
		ans.push_back(e);
		dfs(e, root, v);
		if (b)break;
		ans.pop_back();
	}
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int h, w, n; cin >> h >> w >> n;
	map<int, set<int>>mpx, mpy;
	vector<int>x(n), y(n);
	rep(i, n) {
		cin >> x[i] >> y[i];
		x[i]--; y[i]--;
		mpx[x[i]].insert(i);
		mpy[y[i]].insert(i);
	}
	scc_graph ss(2 * n);
	rep(i, n) {
		for (auto idx : mpy[y[i]]) {
			if (i == idx) continue;
			to[i * 2].push_back(idx * 2 + 1);
			ss.add_edge(i * 2, idx * 2 + 1);
		}
		for (auto idx : mpx[x[i]]) {
			if (i == idx) continue;
			to[i * 2 + 1].push_back(idx * 2);
			ss.add_edge(i * 2 + 1, idx * 2);
		}
	}
	vector<vector<int>> scc = ss.scc();
	rep(i, scc.size()) {
		if (1 == scc[i].size())continue;
		int fir = -1;
		rep(j, scc[i].size()) {
			if (0 == scc[i][j] % 2)fir = scc[i][j];
		}
		rep(j, n * 2)use[j] = true;
		rep(j, scc[i].size())use[scc[i][j]] = false;
		ans.push_back(fir);
		dfs(fir, fir);
		cout << ans.size() << endl;
		rep(j, ans.size()) 	cout << ans[j] / 2 + 1 << " ";
		return 0;
	}
	cout << -1 << endl;
	return 0;
}