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

using graph = vector<vector<int>>;

vector<int> cycle;

void dfs(const graph &to, vector<bool> &seen, int v, int p)
{
    seen.at(v) = true;
    for (auto &&c : to.at(v))
    {
        if (not cycle.empty())
        {
            break;
        }
        if (c == p)
        {
            continue;
        }
        if (seen.at(c))
        {
            cycle.push_back(c);
            break;
        }
        dfs(to, seen, c, v);
    }
    if (not cycle.empty())
    {
        cycle.push_back(v);
    }
}

int main()
{
    int h, w, n;
    cin >> h >> w >> n;
    graph to(h + w + n);
    for (int i = 0; i < n; i++)
    {
        int x, y;
        cin >> x >> y;
        x--;
        y--;
        to.at(x).push_back(h + w + i);
        to.at(h + w + i).push_back(x);
        to.at(y + h).push_back(h + w + i);
        to.at(h + w + i).push_back(y + h);
    }

    vector<bool> seen(h + w + n);
    for (int i = 0; i < h + w + n; i++)
    {
        if (seen.at(i))
        {
            continue;
        }
        dfs(to, seen, i, -1);
    }

    if (cycle.empty())
    {
        cout << -1 << endl;
        return 0;
    }

    vector<int> ans;
    int len = cycle.size(), shift = -1;
    for (int i = 0; i < len; i++)
    {
        if (i and cycle.at(i) == cycle.at(0))
        {
            break;
        }
        if (cycle.at(i) >= h + w)
        {
            ans.push_back(cycle.at(i) - h - w);
        }
        else if (shift == -1)
        {
            shift = (ans.size() + (cycle.at(i) >= h)) % 2;
        }
    }
    rotate(ans.begin(), ans.begin() + shift, ans.end());
    int k = ans.size();
    cout << k << endl;
    for (int i = 0; i < k; i++)
    {
        cout << ans.at(i) + 1;
        if (i < k - 1)
        {
            cout << ' ';
        }
        else
        {
            cout << endl;
        }
    }

    return 0;
}