#include <bits/stdc++.h>

using namespace std;

#define INFILE "cuplaj.in"
#define OUTFILE "cuplaj.out"

const int N_MAX = 1e5;

int nodesLeft, nodesRight, edges;
int lft[N_MAX + 1], rgt[N_MAX + 1];
bool visited[N_MAX + 1];
vector<int> adj[N_MAX + 1];

void connect(int node1, int node2){
    lft[node1] = node2;
    rgt[node2] = node1;
}

bool link(int node){
    if(visited[node]) return false;
    visited[node] = true;
    for(auto &to : adj[node]){
        if(!rgt[to]) {
            connect(node, to);
            return true;
        }
    }
    for(auto &to : adj[node]){
        if(link(rgt[to])){
            connect(node, to);
            return true;
        }
    }
    return false;
}

void solve(){

    cin >> nodesLeft >> nodesRight >> edges;
    for(int i = 0; i < edges; ++i){
        int node1, node2; cin >> node1 >> node2;
        adj[node1].push_back(node2);
    }

    bool ok = true;
    while(ok) {
        ok = false;
        memset(visited, false, sizeof visited);
        for(int i = 1; i <= nodesLeft; ++i){
            if(!lft[i]) ok |= link(i);
        }
    }

    int ans = 0;
    for(int i = 1; i <= nodesLeft; ++i){
        if(lft[i]) ++ans;
    }

    cout << ans << '\n';
    for(int i = 1; i <= nodesLeft; ++i){
        if(lft[i]) cout << i << " " << lft[i] << '\n';
    }

}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    freopen(INFILE, "r", stdin);
    freopen(OUTFILE, "w", stdout);
    solve();
    return 0;
}