#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;

vector<int> g[200000];
bool used[200000];
int pre[200000];

vector<int> ans;
void make_loop(int v, int end){
    while(v != end){
        ans.push_back(v);
        v = pre[v];
    }
    ans.push_back(end);
}

bool dfs(int v){
    used[v] = true;
    for(int to: g[v]){
        if(!used[to]){
            pre[to] = v;
            if(dfs(to)) return true;
        }else if(pre[v] != to){
            make_loop(v, to);
            return true;
        }
    }
    return false;
}

using P = pair<int, int>;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    int h, w; cin >> h >> w;
    int n; cin >> n;
    map<P, int> idx;
    vector<int> x(n), y(n);
    for(int i = 0; i < n; i++){
        cin >> x[i] >> y[i];
        x[i]--; y[i]--;
        g[x[i]].push_back(h+y[i]);
        g[h+y[i]].push_back(x[i]);
        idx[P(x[i], h+y[i])] = i;
        idx[P(h+y[i], x[i])] = i;
    }

    for(int i = 0; i < h+w; i++){
        if(!used[i]){
            if(dfs(i)){
                int m = ans.size();
                cout << m << endl;
                vector<int> v(m);
                for(int j = 0; j < m; j++){
                    int k = (j+1)%m;
                    v[j] = idx[P(ans[j], ans[k])];
                }
                if(x[v[0]] != x[v[1]]){
                    for(int j = 0; j < m; j++) cout << v[j]+1 << ' ';
                    cout << endl;
                }else{
                    for(int j = 0; j < m; j++) cout << v[(j+1)%m]+1 << ' ';
                    cout << endl;
                }
                // for(int j: v) cout << x[j] << ' ' << y[j] << endl;
                return 0;
            }
        }
    }
    cout << -1 << endl;
}