#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define FORR2(x,y,arr) for(auto& [x,y]:arr)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
template<class T> bool chmax(T &a, const T &b) { if(a<b){a=b;return 1;}return 0;}
template<class T> bool chmin(T &a, const T &b) { if(a>b){a=b;return 1;}return 0;}
//-------------------------------------------------------

int H,W,N;
int X[202020],Y[202020];

vector<int> R[202020];
vector<int> C[202020];

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>H>>W>>N;
	FOR(i,N) {
		cin>>Y[i]>>X[i];
		Y[i]--,X[i]--;
		C[X[i]].push_back(i);
	}
	
	FOR(x,W) if(C[x].size()>=2) {
		FORR(i,C[x]) R[Y[i]].push_back(i);
	}
	
	FOR(y,H) if(R[y].size()>=2) {
		vector<int> ret={0,R[y][0],R[y][1],0};
		FORR(c,C[X[R[y][0]]]) if(c!=R[y][0]) ret[0]=c;
		FORR(c,C[X[R[y][1]]]) if(c!=R[y][1]) ret[3]=c;
		
		cout<<4<<endl;
		FORR(r,ret) cout<<(r+1)<<" ";
		cout<<endl;
		return;
	}
	cout<<-1<<endl;
	
	
	
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}