/*
--------------              |   /
      |                     |  /
      |                     | /
      |             *       |/          |    |         ------            *
      |                     |           |    |        /      \
      |             |       |\          |    |       |       |\          |
   \  |             |       | \         |    |       |       | \         |
    \ |             |       |  \        |    |        \     /   \        |
     V              |       |   \        \__/|         -----     \       |
*/
#include <bits/stdc++.h>
using namespace std;
#define debug(x) cerr << "\e[1;31m" << #x << " = " << (x) << "\e[0m\n"
#define print(x) emilia_mata_tenshi(#x, begin(x), end(x))
template<typename T> void emilia_mata_tenshi(const char *s, T l, T r) {
	cerr << "\e[1;33m" << s << " = [";
	while(l != r) {
		cerr << *l;
		cerr << (++l == r ? ']' : ',');
	}
	cerr << "\e[0m\n";
}

#define EmiliaMyWife ios::sync_with_stdio(0); cin.tie(NULL);
using ll = int64_t;
using ull = uint64_t;
using ld = long double;
using uint = uint32_t;
const double EPS  = 1e-8;
const int INF     = 0x3F3F3F3F;
const ll LINF     = 4611686018427387903;
const int MOD     = 1e9+7;
/*--------------------------------------------------------------------------------------*/

signed main() { EmiliaMyWife
	int h, w, n;
	cin >> h >> w >> n;
	vector<vector<pair<int, int>>> arr(w + 1);
	for(int i = 0; i < n; i++) {
		int x, y;
		cin >> y >> x;
		arr[x].push_back({y, i + 1});
	}
	vector<pair<int, int>> has(h + 1, {-1, -1});
	for(const auto &a : arr) {
		if(a.size() <= 1)
			continue;
		for(int i = 0; i < a.size(); i++) {
			if(~has[a[i].first].first) {
				cout << "4\n";
				cout << has[a[i].first].second << ' ' << has[a[i].first].first << ' ';
				cout << a[i].second << ' ' << a[(i + 1) % a.size()].second << '\n';
				return 0;
			}
		}
		for(int i = 0; i < a.size(); i++) {
			has[a[i].first] = {a[i].second, a[(i + 1) % a.size()].second};
		}
	}
	cout << "-1\n";
}