#include<bits/stdc++.h>
using namespace std;
//#define int long long
#define REP(i,m,n) for(int i=(m);i<(n);i++)
#define rep(i,n) REP(i,0,n)
#define pb push_back
#define all(a) a.begin(),a.end()
#define rall(c) (c).rbegin(),(c).rend()
#define mp make_pair
#define endl '\n'
//#define vec vector<ll>
//#define mat vector<vector<ll> >
#define fi first
#define se second
#define double long double
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> pll;
//typedef long double ld;
typedef complex<double> Complex;
const ll INF=1e9+7;
const ll MOD=998244353;
const ll inf=INF*INF;
const ll mod=MOD;
const ll MAX=200010;
const double PI=acos(-1.0);
typedef vector<vector<ll> > mat;
typedef vector<ll> vec;

vector<vector<ll> > G(MAX);
vector<ll>ans(0);
vector<ll>used(MAX);
ll st=-1;
ll cnt=0;
void dfs(ll i, ll p){
    used[i]=1;
    for(auto e:G[i]){
        if(e==p)continue;
        if(used[e]==1){
            st=e;
            ans.pb(e);
            break;
        }
        dfs(e,i);
        if(st!=-1)break;
    }
    if(st==-2)return;
    if(st!=-1)ans.pb(i);
    if(st==i)st=-2;
}

signed main(){
    ll h,w,n;cin>>h>>w>>n;
    map<pll,ll>ma;
    ll m=-1;
    rep(i,n){
        ll x,y;cin>>x>>y;
        x--;y--;
        G[x].pb(h+y);
        G[h+y].pb(x);
        ma[mp(x,h+y)]=i;
        ma[mp(h+y,x)]=i;
    }
    rep(i,h+w){
        if(used[i])continue;
        dfs(i,-1);
        if(st!=-1)break;
    }
    if(st==-1){
        cout<<-1<<endl;
    }else{
        cout<<ans.size()-1<<endl;
        rep(i,ans.size()-1){
            cout<<ma[mp(ans[i],ans[i+1])]+1<<' ';
        }
        cout<<endl;
    }
}