#include <bits/stdc++.h>
using namespace std;
int main(){
    int H, W, N;
    cin >> H >> W >> N;
    vector<int> x(N), y(N);
    vector<vector<int>> G(H + W);
    map<pair<int, int>, int> m;
    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]);
        m[{x[i], H + y[i]}] = i;
    }
    vector<int> used(H + W);
    vector<int> par(H + W, -1);
    bool f = false;
    auto dfs = [&](auto dfs, int now, int num, int p) -> void{
        used[now] = num;
        if(f) true;
        for(int to : G[now]){
            if(f) return;
            if(p == to) continue;
            if(used[to] == -1) continue;
            if(used[to] > 0 && num - used[to] >= 3){
                f = true;
                int t = now;
                vector<int> ans;
                ans.push_back(m[{min(now, to), max(now, to)}]);
                while(par[t] != -1){
                    ans.push_back(m[{min(t, par[t]), max(t, par[t])}]);
                    t = par[t];
                }
                reverse(ans.begin(), ans.end());
                cout << ans.size() << endl;
                for(int i = 0; i < (int)ans.size(); i++){
                    if(i == (int)ans.size() - 1) cout << ans[i] + 1 << endl;
                    else cout << ans[i] + 1 << ' ';
                }
                return;
            }
            par[to] = now;
            dfs(dfs, to, num + 1, now);
        }
        used[now] = -1;
    };
    for(int i = 0; i < H; i++){
        if(used[i] == 0) dfs(dfs, i, 1, -1);
    }
    if(!f) cout << -1 << endl;

}