#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
constexpr int N = 1e5 + 5;
vector < int > g[N];
int l, r, m, mch[N], vis[N];
int dfs(int u, int t) {
  if (vis[u] == t) return 0;
  vis[u] = t;
  for (int v : g[u]) {
    if (!~mch[v] || dfs(mch[v], t)) return mch[v] = u, 1;
  }
  return 0;
}

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  cin >> l >> r >> m;
  memset(mch, -1, sizeof(mch));
  memset(vis, -1, sizeof(vis));
  for (int i = 1, u, v; i <= m; i++) {
    cin >> u >> v;
    g[u].push_back(v);
  }
  int ret = 0;
  vector < int > ord(l);
  iota(ord.begin(), ord.end(), 0);
  mt19937 rng(random_device{}());
  shuffle(ord.begin(), ord.end(), rng);
  for (int i : ord) ret += dfs(i, i);
  cout << ret << '\n';
  for (int i = 0; i < r; i++) {
    if (~mch[i]) cout << mch[i] << ' ' << i << '\n';
  }
  return 0;
}