#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=r-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define vtpl(x,y,z) vector<tuple<x,y,z>>
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
const ll dy[9]={0,1,-1,0,1,1,-1,-1,0};
const ll dx[9]={1,0,0,-1,1,-1,1,-1,0};
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

vvpl g(200010);
vl seen(200010);
vl fin(200010);
vl hist;
ll pos=-1;
void dfs(ll v,ll p){
  seen[v]=1;
  //hist.push_back(v);
  for(auto nv:g[v]){
    if(nv.first==p)continue;
    if(fin[nv.first])continue;
    if(seen[nv.first]&&!fin[nv.first]){
      pos=nv.first;
      hist.push_back(nv.second);
      return;
    }
    hist.push_back(nv.second);
    dfs(nv.first,v);
    if(pos!=-1)return;
    hist.pop_back();
  }
  fin[v]=1;
}
int main(){
    ll h,w,n;cin >> h >> w >>n;
    rep(i,n){
        ll x,y;cin >> x >> y;x--;y--;
        g[x].push_back({y+h,i+1});
        g[y+h].push_back({x,i+1});
    }
    rep(i,h){
      if(seen[i])continue;
      dfs(i,-1);
      if(hist.size()){
        cout << hist.size() <<endl;
        for(auto p:hist)cout << p <<" ";cout << endl;
        return 0;
      }
    }
    cout << -1 <<endl;
}