#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
int H,W,N;
int X[1<<17],Y[1<<17];
vector<int>G[3<<17];
vector<int>tmp;
vector<int>ans;
int vis[3<<17];
bool dfs(int u,int p)
{
	vis[u]=tmp.size();
	tmp.push_back(u);
	for(int v:G[u])if(v!=p)
	{
		if(vis[v]==-1)
		{
			if(dfs(v,u))return true;
		}
		else
		{
			ans=vector<int>(tmp.begin()+vis[v],tmp.end());
			return true;
		}
	}
	tmp.pop_back();
	return false;
}
main()
{
	cin>>H>>W>>N;
	for(int i=0;i<N;i++)
	{
		cin>>X[i]>>Y[i];
		X[i]--,Y[i]--;
		G[i].push_back(N+X[i]);
		G[i].push_back(N+H+Y[i]);
		G[N+X[i]].push_back(i);
		G[N+H+Y[i]].push_back(i);
	}
	for(int i=0;i<N+H+W;i++)vis[i]=-1;
	for(int i=0;i<N;i++)if(vis[i]==-1)
	{
		if(dfs(i,-1))
		{
			vector<int>ret;
			for(int id:ans)if(id<N)ret.push_back(id);
			if(X[ret[0]]==X[ret[1]])
			{
				ret.push_back(ret[0]);
				ret.erase(ret.begin());
			}
			cout<<ret.size()<<endl;
			for(int i=0;i<ret.size();i++)cout<<ret[i]+1<<(i+1==ret.size()?"\n":" ");
			return 0;
		}
	}
	cout<<-1<<endl;
}