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#include <bits/stdc++.h>
#define F first
#define S second
#define mp make_pair
#define pb push_back
#define INF 0x3f3f3f3f
#define LINF 0x3f3f3f3f3f3f3f3fLL

using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef set<int> si;
typedef pair<int,int> ii;
typedef vector<ii> vii;
typedef map<string,int> msi;
typedef map<int,int> mi;

int n1,n2,d;

vi grafo[100010];
int vis[100010];
int pd[100010];

int dfs(int pai){
    if(pd[pai]!= -1) return pd[pai];
    int cont=0;
    for(int i =0;i<grafo[pai].size();i++){
        int filho = grafo[pai][i];
        //if(!vis[filho]){
            int x= dfs(filho);
            if((pai < n1 && filho>=n1) || (filho < n1 && pai>=n1)) x+=1;
            cont = max(x,cont);
        //}
    }
    return pd[pai]=cont;
}

int main(){
    while(cin >>n1>>n2>>d && n1){
        for(int i =0;i<n1+n2;i++){
            grafo[i].clear();
        }
        while(d--){
            int x,y;
            cin >>x >>y;
            x--;
            y--;
            grafo[y].pb(x);
        }
        memset(vis,0,sizeof vis);
        int cont1 =0;
        memset(pd,-1,sizeof pd);
        for(int i =0;i<n1;i++){
            if(!vis[i])
                cont1= max(dfs(i),cont1);
        }
        int cont2 =0;
        for(int i =n1;i<n1+n2;i++){
            if(!vis[i])
                cont2 = max(cont2,dfs(i));
        }
        cont1 = min(cont1,cont2)+3;
        //if(cont1 >(n1+n2)/2)cont1--;
        cout  <<cont1 <<'\n';
    }
    return 0;
}