#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#include <list>
#include <atcoder/all>
#define popcount __builtin_popcount
using namespace std;
using namespace atcoder;
typedef long long ll;
typedef pair<int, int> P;
struct unionfind{
    vector<int> par, sz;
    unionfind() {}
    unionfind(int n):par(n), sz(n, 1){
        for(int i=0; i<n; i++) par[i]=i;
    }
    int find(int x){
        if(par[x]==x) return x;
        return par[x]=find(par[x]);
    }
    void unite(int x, int y){
        x=find(x); y=find(y);
        if(x==y) return;
        if(sz[x]>sz[y]) swap(x, y);
        par[x]=y;
        sz[y]+=sz[x];
    }
    bool same(int x, int y){
        return find(x)==find(y);
    }
    int size(int x){
        return sz[find(x)];
    }
};
int main()
{
    int h, w, n;
    cin>>h>>w>>n;
    int x[100010], y[100010];
    int n1=100000;
    vector<P> g[200020];
    unionfind uf(2*n1);
    vector<int> ans;
    int par[200020];
    auto dfs=[&](auto dfs, int x, int p)->void{
        for(auto q:g[x]){
            if(q.first==p){
                par[x]=q.second;
            }else{
                dfs(dfs, q.first, x);
            }
        }
    };
    for(int i=0; i<n; i++){
        cin>>x[i]>>y[i];
        x[i]--; y[i]--;
        if(uf.same(x[i], y[i]+n1)){
            dfs(dfs, y[i]+n1, -1);
            int v=x[i];
            while(v!=y[i]+n1){
                ans.push_back(par[v]);
                if(v<n1){
                    v=y[par[v]]+n1;
                }else{
                    v=x[par[v]];
                }
            }
            ans.push_back(i);
            reverse(ans.begin(), ans.end());
            cout<<ans.size()<<endl;
            for(int i=0; i<ans.size(); i++){
                cout<<ans[i]+1;
                if(i<(int)ans.size()-1) cout<<" ";
            }
            cout<<endl;
            return 0;
        }
        uf.unite(x[i], y[i]+n1);
        g[x[i]].push_back({y[i]+n1,i});
        g[y[i]+n1].push_back({x[i],i});

    }
    cout<<-1<<endl;
    return 0;
}