#include <bits/stdc++.h>
#define LL long long
#define sl(n) strlen(n)
#define endline puts("")
#define pii pair<int , int>
#define pr_q priority_queue
#define debug puts("DEBUG.")
using namespace std;
const int N = 2e5 + 10;
const int inf = ~0u >> 2;
int n1,n2,m;
int cnt,hd[N];
struct edge
{
	int v,nxt;
}e[N];
void add(int u , int v)
{
	++cnt,e[cnt].v = v;
	e[cnt].nxt = hd[u],hd[u] = cnt;
}
int vis[N],mat[N];
bool dfs(int u , int c)
{
	if(vis[u] == c)
		return 0;
	vis[u] = c;
	for(int i = hd[u];i;i = e[i].nxt)
	{
		int v = e[i].v;
		if( !mat[v] || dfs(mat[v] , c) )
			return mat[v] = u;
	}
	return 0;
}
int main()
{
	cin >> n1 >> n2 >> m;
	for(int i = 1,u,v;i <= m;i++)
		scanf("%d%d" , &u , &v),++u,++v,add(u , v);
	int res = 0;
	for(int i = 1;i <= n1;i++)
		res += dfs(i , i);
	cout << res << endl;
	for(int i = 1;i <= n2;i++)
		if( mat[i] )
			printf("%d %d\n" , mat[i] - 1 , i - 1);
	return 0;
}