#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll=long long;
#define MOD 998244353
using Graph=vector<vector<pair<int,int>>>;
#define INF 1000000000
#define MAX 200000

vector<int> ans;

bool dfs(Graph &G,int v,int p,vector<int> &seen,int &g){
  seen[v]=1;
  for(auto e:G[v]){
    int nv=e.first;
    if(nv==p){
      continue;
    }
    if(seen[nv]==1){
      g=nv;
      ans.push_back(e.second);
      return true;
    }else{
      if(dfs(G,nv,v,seen,g)){
        if(g!=-1){
          ans.push_back(e.second);
          if(g==v){
            g=-1;
          }
        }
        return true;
      }
    }
  }
  return false;
}

int main(){
  int H,W,N;
  cin>>H>>W>>N;
  vector<int> x(N),y(N);
  Graph G(H+W);
  for(int i=0;i<N;i++){
    cin>>x[i]>>y[i];
    x[i]--;y[i]--;
    G[x[i]].push_back(make_pair(H+y[i],i));
    G[H+y[i]].push_back(make_pair(x[i],i));
  }

  vector<int> seen(H+W,0);
  for(int i=0;i<H+W;i++){
    if(seen[i]==0){
      int g=-1;
      if(dfs(G,i,-1,seen,g)){
        cout<<ans.size()<<'\n';
        if(y[ans[0]]==y[ans[1]]){
          for(int j=0;j<ans.size();j++){
            cout<<ans[j]+1<<' ';
          }
          cout<<'\n';
        }else{
          for(int j=0;j<ans.size();j++){
            cout<<ans[(j+1)%(int)ans.size()]+1<<' ';
          }
          cout<<'\n';
        }
        return 0;
      }
    }
  }
  cout<<-1<<'\n';
}