#include <fstream>
#include <iostream>
#include <vector>
using namespace std;

ifstream f("cuplaj.in");
ofstream g("cuplaj.out");

#define foor(it,v) for(__typeof(v.begin())it=v.begin();it!=v.end();++it)
#define cout g

int n,m,e,i,x,y,nrc;
vector<vector<int> >G;
vector<int> L,R;

bool pair_up(int nod)
{
    foor(it,G[nod]) if(L[*it]==0)
    {
        L[*it]=nod;
        R[nod]=*it;
        return true;
    }

    foor(it,G[nod]) if(L[*it]!=nod)
                    if(pair_up(L[*it]))
    {
        L[*it]=nod;
        R[nod]=*it;
        return true;
    }

    return false;
}

int main()
{
    f>>n>>m>>e;
    G.resize(n+1);
    R.resize(n+1);
    L.resize(m+1);
    for(;e;--e)
    {
        f>>x>>y;
        G[x].push_back(y);
    }
    for(i=1;i<=n;++i) if(R[i]==0) pair_up(i);
    for(i=1;i<=n;++i) if(R[i]) ++nrc;
    cout<<nrc<<'\n';
    for(i=1;i<=n;++i) if(R[i]) cout<<i<<' '<<R[i]<<'\n';
    return 0;
}