#include<bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using mint=modint998244353; //1000000007;
using ll=long long;
using pp=pair<int,int>;
#define sr string 
#define vc vector
#define fi first
#define se second
#define rep(i,n) for(int i=0;i<(int)n;i++)
#define pb push_back
#define all(v) v.begin(),v.end()
#define pque priority_queue
#define bpc(a) __builtin_popcount(a)
int main(){
  int h,w,n;cin>>h>>w>>n;
  vc v(h+w,vc<int>(0));
  map<pp,int>m;
  rep(i,n){
    int x,y;cin>>x>>y;
    x--; y--;
    v[x].pb(h+y); v[h+y].pb(x);
    m[{x,y+h}]=i; m[{y+h,x}]=i;
  }
  vc<bool>ch(h+w,false);
  vc<int>ans;
  auto f=[&](auto f,int a,int p)->int{
    if(ch[a])return a;
    ch[a]=true;
    int res=-1;
    for(auto au:v[a])if(au!=p){
      res=f(f,au,a);
      if(res==-2)return -2;
      if(res!=-1)break;
    }
    if(res!=-1)ans.pb(a);
    if(res==a)res=-2;
    return res;
  };
  rep(i,h)if(!ch[i]){
    f(f,i,-1);
    if(ans.size())break;
  }
  if(!ans.size()){
    cout<<-1;
    return 0;
  }
  cout<<ans.size()<<"\n";
  if(ans[0]>=h){
    ans.pb(ans[0]); ans.pb(ans[1]);
    for(int i=1;i<ans.size()-1;i++)cout<<m[{ans[i],ans[i+1]}]+1<<' ';
  }
  else{
    ans.pb(ans[0]);
    rep(i,ans.size()-1)cout<<m[{ans[i],ans[i+1]}]+1<<' ';
  }
}