#include <bits/stdc++.h>

using namespace std;

vector<int> Match(vector<vector<int>>& graph, int n, int m) {
  vector<int> l(n, -1), r(m, -1), q, dist;
  for (int ch = 1; ch--; ) {
    dist.assign(n, -1); q.clear();
    for (int i = 0; i < n; ++i)
      if (l[i] == -1)
        dist[i] = 0, q.push_back(i);
    for (int i = 0; i < (int)q.size(); ++i)
      for (auto v : graph[q[i]])
        if (r[v] != -1 && dist[r[v]] == -1)
          dist[r[v]] = 1 + dist[q[i]], q.push_back(r[v]);
    reverse(q.begin(), q.end());
    for (auto u : q) for (auto v : graph[u])
      if (r[v] == -1 || (
          dist[r[v]] == 1 + dist[u] && l[r[v]] != v)) {
        ch |= l[u] == -1; l[u] = v; r[v] = u; break;
      }
    for (int i = 0; i < m; ++i)
      if (r[i] != -1 && l[r[i]] != i)
        r[i] = -1;
  }
  return l;
}

int main() {
  ifstream cin("cuplaj.in");
  ofstream cout("cuplaj.out");

  int n, m, k; cin >> n >> m >> k;
  vector<vector<int>> graph(n);
  for (int i = 0; i < k; ++i) {
    int a, b; cin >> a >> b; --a; --b; 
    graph[a].push_back(b);
  }
  
  auto ltor = Match(graph, n, m);
  int ans = 0;
  for (int i = 0; i < n; ++i) 
    ans += ltor[i] != -1;
  cout << ans << '\n';
  for (int i = 0; i < n; ++i)
    if (ltor[i] != -1)
      cout << i + 1 << " " << ltor[i] + 1 << '\n';
  return 0;
}