//g++ 1.cpp -std=c++14 -O2 -I .
#include <bits/stdc++.h>
using namespace std;

#include <atcoder/all>
using namespace atcoder;

using ll = long long;
using ld = long double;

using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vld = vector<ld>;
using vvld = vector<vld>;

#define fi first
#define se second
#define pb push_back
#define pq_big(T) priority_queue<T,vector<T>,less<T>>
#define pq_small(T) priority_queue<T,vector<T>,greater<T>>
#define all(a) a.begin(),a.end()
#define rep(i,start,end) for(ll i=start;i<(ll)(end);i++)
#define per(i,start,end) for(ll i=start;i>=(ll)(end);i--)

vi seen(410000,0);
vi fin(410000,0);
vi hist;
int pos=-1;

void dfs(vvi &g,int now,int p){
  seen[now]=1;
  hist.pb(now);

  for(int next:g[now]){
    if(next==p){
      continue;
    }
    if(fin[next]==1){
      continue;
    }
    if(seen[next]==1&&fin[next]==0){
      pos=next;
      return;
    }

    dfs(g,next,now);

    if(pos!=-1){
      return;
    }
  }

  hist.pop_back();
  fin[now]=1;
}

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  int h,w,n;
  cin>>h>>w>>n;

  vvi g(h+w);
  vector<pair<int,int>> place(n);
  map<pair<int,int>,int> inv;

  rep(i,0,n){
    int x,y;
    cin>>x>>y;
    x--;y--;
    place[i].fi=x,place[i].se=y;
    g[x].pb(h+y);
    g[h+y].pb(x);
    inv[{x,h+y}]=i;
    inv[{h+y,x}]=i;
  }

  rep(i,0,h+w){
    if(seen[i]==1)continue;
    if(g[i].size()==0)continue;

    dfs(g,i,-1);

    if(pos!=-1){
      break;
    }
  }

  if(pos==-1){
    cout<<"-1\n";
    return 0;
  }

  vi cycle;
  while(!hist.empty()){
    int t=hist[hist.size()-1];
    cycle.pb(t);
    hist.pop_back();
    if(t==pos){
      break;
    }
  }

  vi ans;
  rep(i,0,cycle.size()){
    int now=cycle[i],next=cycle[(i+1)%cycle.size()];
    ans.pb(inv[{now,next}]);
  }

  cout<<ans.size()<<"\n";

  if(place[ans[0]].se==place[ans[1]].se){
    rep(i,0,ans.size()){
      cout<<ans[i]+1<<" ";
    }
    cout<<"\n";
  }
  else{
    rep(i,1,ans.size()+1){
      cout<<ans[i%ans.size()]+1<<" ";
    }
    cout<<"\n";
  }
}