#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000001

vector<int> ans;
vector<bool> f;
bool dfs(vector<vector<pair<int,int>>> &E,int cur,int p){
	f[cur] = true;
	
	rep(i,E[cur].size()){
		int to = E[cur][i].first;
		if(to==p)continue;
		if(f[to]){
			ans.push_back(E[cur][i].second);
			return true;
		}
		if(dfs(E,to,cur)){
			ans.push_back(E[cur][i].second);
			return true;
		}
	}
	return false;
}

int main(){
	
	int H,W;
	cin>>H>>W;
	
	int N;
	cin>>N;
	
	dsu D(H+W);
	vector<int> x,y;
	rep(i,N){
		int a,b;
		scanf("%d %d",&a,&b);
		a--;b--;
		a = a,b = H+b;
		x.push_back(a);
		y.push_back(b);
		
		if(D.same(a,b)){
			for(int j=i+1;j<N;j++){
				cin>>a>>b;
			}
			break;
		}
		D.merge(a,b);
		if(i==N-1){
			cout<<-1<<endl;
			return 0;
		}
	}
	N = x.size();
	
	
	vector<int> ind;
	rep(i,H+W){
		if(D.same(i,x.back()))ind.push_back(i);
	}
	//cout<<ind.size()<<endl;
	vector<vector<pair<int,int>>> E(ind.size());
	rep(i,N){
		if(D.same(x[i],x.back())){
			int a = distance(ind.begin(),lower_bound(ind.begin(),ind.end(),x[i]));
			int b = distance(ind.begin(),lower_bound(ind.begin(),ind.end(),y[i]));
			E[a].emplace_back(b,i);
			E[b].emplace_back(a,i);
		}
	}
	f.resize(ind.size(),false);
	
	dfs(E,0,-1);
	
	dsu DD(H+W);
	vector<int> Ans;
	rep(i,ans.size()){
		Ans.push_back(ans[i]);
		int a = x[ans[i]],b = y[ans[i]];
		if(DD.same(a,b)){
			break;
		}
		DD.merge(a,b);
	}
	
	if(x[Ans[0]]==x[Ans[1]]){
		int t = Ans.back();
		Ans.pop_back();
		Ans.insert(Ans.begin(),t);
	}
	
	cout<<Ans.size()<<endl;
	rep(i,Ans.size()){
		if(i!=0)cout<<' ';
		cout<<Ans[i]+1;
	}
	cout<<endl;
	
	return 0;
}