#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;

//template
#define rep(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define ALL(v) (v).begin(),(v).end()
using ll=long long int;
const int inf = 0x3fffffff; const ll INF = 0x1fffffffffffffff; const double eps=1e-12;
template<typename T>inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<typename T>inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}

struct UnionFind{
   vector<int> par; int n;
   UnionFind(){}
   UnionFind(int _n):par(_n,-1),n(_n){}
   int root(int x){return par[x]<0?x:par[x]=root(par[x]);}
   bool same(int x,int y){return root(x)==root(y);}
   int size(int x){return -par[root(x)];}
   bool unite(int x,int y){
      x=root(x),y=root(y); if(x==y)return false;
      if(size(x)>size(y))swap(x,y);
      par[y]+=par[x]; par[x]=y; n--; return true;
   }
};

using P=pair<int,int>;
vector<P> g[201010];
bool dfs(int v,int p,int tar,vector<int>& path){
   if(v==tar)return true;
   for(auto& [to,id]:g[v])if(to!=p){
      path.push_back(id);
      if(dfs(to,v,tar,path))return true;
      path.pop_back();
   }
   return false;
}

int main(){
   int h,w,n;
   cin>>h>>w>>n;
   vector<int> x(n),y(n);
   rep(i,0,n){
      cin>>x[i]>>y[i];
      x[i]--; y[i]--;
   }

   UnionFind uni(h+w);
   rep(i,0,n){
      if(uni.unite(x[i],y[i]+h)){
         g[x[i]].push_back({y[i]+h,i});
         g[y[i]+h].push_back({x[i],i});
      }
      else{
         vector<int> res,add;
         int rt=uni.root(x[i]);
         dfs(rt,-1,x[i],res);
         dfs(rt,-1,y[i]+h,add);
         reverse(ALL(res));
         res.insert(res.end(),ALL(add));
         
         if(x[i]!=x[res.front()]){
            reverse(ALL(res));
            res.push_back(i);
            reverse(ALL(res));
         }
         else res.push_back(i);
         
         cout<<res.size()<<'\n';
         rep(j,0,res.size())cout<<res[j]+1<<(j==res.size()-1?'\n':' ');
         return 0;
      }
   }
   puts("-1");
   return 0;
}