#pragma GCC target("avx2")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
#define DEBUG
#ifdef DEBUG
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
    os << '(' << p.first << ',' << p.second << ')';
    return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
    os << '{';
    for(int i = 0; i < (int)v.size(); i++) {
        if(i) { os << ','; }
        os << v[i];
    }
    os << '}';
    return os;
}
void debugg() { cerr << endl; }
template <class T, class... Args>
void debugg(const T &x, const Args &... args) {
    cerr << " " << x;
    debugg(args...);
}
#define debug(...)                                                             \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]: ", debugg(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef pair<ll,ll> P;
typedef pair<int,int> pii;
typedef vector<P> vpl;
typedef tuple<ll,ll,ll> tapu;
#define rep(i,n) for(int i=0; i<(n); i++)
#define REP(i,a,b) for(int i=(a); i<(b); i++)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
const int inf = (1<<30)-1;
const ll linf = 1LL<<61;
const int MAX = 25000000;
int dy[8] = {0,1,0,-1,1,-1,-1,1};
int dx[8] = {-1,0,1,0,1,-1,1,-1};
const double pi = acos(-1);
const double eps = 1e-7;
template<typename T1,typename T2> inline bool chmin(T1 &a,T2 b){
	if(a>b){
		a = b; return true;
	}
	else return false;
}
template<typename T1,typename T2> inline bool chmax(T1 &a,T2 b){
	if(a<b){
		a = b; return true;
	}
	else return false;
}
template<typename T> inline void print(T &a){
    int sz = a.size();
    for(auto itr = a.begin(); itr != a.end(); itr++){
		cout << *itr;
        sz--;
        if(sz) cout << " ";
	}
    cout << "\n";
}
template<typename T1,typename T2> inline void print2(T1 a, T2 b){
	cout << a << " " << b << "\n";
}
template<typename T1,typename T2,typename T3> inline void print3(T1 a, T2 b, T3 c){
	cout << a << " " << b << " " << c << "\n";
}
void mark() {cout << "#" << "\n";}
ll pcount(ll x) {return __builtin_popcountll(x);}
//const int mod = 1e9 + 7;
const int mod = 998244353;

int main(){
    int h,w,n; cin >> h >> w >> n;
    int N = h+w+n;
    vvl G(N);
    rep(i,n){
        int x,y; cin >> x >> y; x--; y--;
        int z = h+w+i;
        G[y].push_back(z);
        G[z].push_back(y);
        G[h+x].push_back(z);
        G[z].push_back(h+x);
    }
    vb visit(N,false);
    vl ans;
    bool f = true;
    int fi = -1;
    auto dfs = [&](auto &&dfs, int u, int p) -> bool {
        int vi = -1;
        visit[u] = true;
        for(auto v : G[u]){
            if(v == p) continue;
            if(visit[v]){
                vi = v;
                continue;
            }
            if(dfs(dfs,v,u)){
                if(f) ans.push_back(u);
                if(fi == u) f = false;
                return true;
            }
        }
        if(vi == -1) return false;
        ans.push_back(u);
        fi = vi;
        return true;
    };
    if(!dfs(dfs,h+w,-1)) cout << -1 << "\n";
    else{
        vl as;
        for(auto x : ans) if(x >= h+w) as.push_back(x-h-w+1);
        int m = as.size();
        cout << m << "\n";
        rep(i,m) cout << as[i] << " \n"[i==m-1];
    }

}