/*
 * =====================================================================================
 *
 *       Filename:  1669.cpp
 *
 *    Description:
 *
 *        Version:  1.0
 *        Created:  13-11-2015 14:32:49
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:
 *        Company:
 *
 * =====================================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include <algorithm>
#include <vector>
#include <string.h>
#include <math.h>
#include <set>
#include <iostream>
#include <queue>
#include <string>
#include <ctype.h>
#include <stack>
//#include<time.h>
//#include<unordered_map>
#include <map>
//#include <windows.h>

using namespace std;

template< class T > T gcd(T a, T b) { return (b != 0 ? gcd<T>(b, a%b) : a); }

typedef long long int llint;
typedef unsigned long long int ullint;

#define FOR(i,a,b) for(int i = a;i<b;++i)
#define EPS 1e-3
#define INF 100002

int deps[INF];
vector<vector<int> > depsDeste(INF);

inline int solve(int cd, int n1, int n2){
	queue<int> pacotes[2];
	//vector<vector<int> > depsDesteAux = depsDeste;
	int depsAux[n1+n2];
	int ans = 0;

	FOR(i,0,n1+n2) depsAux[i] = deps[i];
	FOR(i,0,n1)
		if(!deps[i]) pacotes[0].push(i);

	FOR(i,n1,n1+n2)
		if(!deps[i]) pacotes[1].push(i);

	//cout<<pacotes[0].size()<< " " << pacotes[0].front()<<endl;
	//cout<<pacotes[1].size()<< " " << pacotes[1].front()<<endl;

	while(!pacotes[0].empty() || !pacotes[1].empty()){
		while(!pacotes[cd].empty()){
			int topo = pacotes[cd].front();
			pacotes[cd].pop();

			FOR(i,0,(int)depsDeste[topo].size()){
				int aux = --depsAux[depsDeste[topo][i]];
				//cout<<"cd: " << cd << " here:"<<depsDeste[topo][i]<< " de quem: "<< topo << " aux: "<<aux<<endl;
				if(!aux)
					if(depsDeste[topo][i]>=n1) pacotes[1].push(depsDeste[topo][i]);
					else pacotes[0].push(depsDeste[topo][i]);
			}
		}
		//cout<<"Simulando "<<cd<<" ans:" <<ans<<endl;
		if(cd) cd = 0;
		else cd = 1;
		ans++;
	}

	return ans+1;
}

int main(){

	ios::sync_with_stdio(false);

	int n1,n2,d;

	while(cin>>n1>>n2>>d){
		if(!n1 && !n2) break;

		memset(deps,0,sizeof deps);
		FOR(i,0,n1+n2+1) depsDeste[i].clear();

		FOR(i,0,d){
			int a,b;
			cin>>a>>b;
			a--, b--;
			deps[a]++;
			depsDeste[b].push_back(a);
		}

		cout << min(solve(0,n1,n2), solve(1,n1,n2)) <<endl;
	}

	return 0;
}