#include <bits/stdc++.h>
using namespace std;
#define rep(i, n)  for(long long i=0;i<(long long)(n);i++)
#define REP(i,k,n) for(long long i=k;i<(long long)(n);i++)
#define pb emplace_back
#define lb(v,k) (lower_bound(all(v),(k))-v.begin())
#define ub(v,k) (upper_bound(all(v),(k))-v.begin())
#define fi first
#define se second
#define pi M_PI
#define PQ(T) priority_queue<T>
#define SPQ(T) priority_queue<T,vector<T>,greater<T>>
#define dame(a) {out(a);return 0;}
#define decimal cout<<fixed<<setprecision(15);
#define all(a) a.begin(),a.end()
#define rsort(a) {sort(all(a));reverse(all(a));}
#define dupli(a) {sort(all(a));a.erase(unique(all(a)),a.end());}
#define popcnt __builtin_popcountll
typedef long long ll;
typedef pair<ll,ll> P;
typedef tuple<ll,ll,ll> PP;
typedef tuple<ll,ll,ll,ll> PPP;
using vi=vector<ll>;
using vvi=vector<vi>;
using vvvi=vector<vvi>;
using vvvvi=vector<vvvi>;
using vp=vector<P>;
using vvp=vector<vp>;
using vb=vector<bool>;
using vvb=vector<vb>;
const ll inf=1001001001001001001;
const ll INF=1001001001;
const ll mod=998244353;
const double eps=1e-10;
template<class T> bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}
template<class T> bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<class T> void out(T a){cout<<a<<'\n';}
template<class T> void outp(T a){cout<<'('<<a.fi<<','<<a.se<<')'<<'\n';}
template<class T> void outvp(T v){rep(i,v.size())cout<<'('<<v[i].fi<<','<<v[i].se<<')';cout<<'\n';}
template<class T> void outvvp(T v){rep(i,v.size())outvp(v[i]);}
template<class T> void outv(T v){rep(i,v.size()){if(i)cout<<' ';cout<<v[i];}cout<<'\n';}
template<class T> void outvv(T v){rep(i,v.size())outv(v[i]);}
template<class T> bool isin(T x,T l,T r){return (l)<=(x)&&(x)<=(r);}
template<class T> void yesno(T b){if(b)out("yes");else out("no");}
template<class T> void YesNo(T b){if(b)out("Yes");else out("No");}
template<class T> void YESNO(T b){if(b)out("YES");else out("NO");}
template<class T> void outset(T s){auto itr=s.begin();while(itr!=s.end()){if(itr!=s.begin())cout<<' ';cout<<*itr;itr++;}cout<<'\n';}
void outs(ll a,ll b){if(a>=inf-100)out(b);else out(a);}
ll gcd(ll a,ll b){if(b==0)return a;return gcd(b,a%b);}
ll modpow(ll a,ll b){ll res=1;a%=mod;while(b){if(b&1)res=res*a%mod;a=a*a%mod;b>>=1;}return res;}

int main(){
    ll h,w,n;cin>>h>>w>>n;
    vvp g(h+w);
    vp v(n);
    rep(i,n){
        ll x,y;cin>>x>>y;
        x--;y--;
        g[x].pb(y+h,i+1);
        g[y+h].pb(x,i+1);
        v[i]=P(x,y);
    }
    vp tmp;
    bool done=false;
    vb seen(h+w,false);
    function<void(ll,ll)> dfs=[&](ll i,ll p){
        seen[i]=true;
        if(done)return;
        for(P x:g[i])if(x.fi!=p){
            if(done)break;
            if(seen[x.fi]){
                vi ans;
                ans.pb(x.se);
                while(tmp.back().fi!=x.fi){
                    ans.pb(tmp.back().se);tmp.pop_back();
                }
                if(v[ans[0]].fi!=v[ans[1]].fi){
                    ll t=ans[0];
                    ans.erase(ans.begin());
                    ans.pb(t);
                }
                out(ans.size());outv(ans);
                done=true;
                break;
            }
            tmp.pb(x);
            dfs(x.fi,i);
            tmp.pop_back();
        }
    };
    rep(i,h+w){
        if(done)break;
        if(!seen[i]){
            tmp.pb(i,-1);
            dfs(i,-1);
        }
    }
    if(!done)out(-1);
}