#include <iostream>
#include <map>
#include <vector>

using namespace std;

int main()
{
    int p, dba, dbe, dbtalalka=0, x, y;
    map <int, int> talalka;
    cin >> p;
    cin >> dba;
    vector <int> idopA;
    for (int i=0; i<dba; i++)
    {
        cin >>idopA[i];
    }
    cin >> dbe;
    vector <int> idopE;
    for (int j=0; j<dbe; j++)
    {
        cin >> idopE[j];
    }
    for (int k=0; k<p; k+=2)
    {
        if (k%2==0)
        {
            if (idopA[k]>idopE[k])
            {
                x=idopA[k];
            }
            else x=idopE[k];
            if (idopA[k+1]>idopE[k+1])
            {
                y=idopE[k+1];
            }
            else y=idopA[k+1];
        }
        talalka[x]=y;
        dbtalalka++;
    }
    cout << dbtalalka<<endl;
    map <int, int>::iterator it=talalka.begin();
    while (it !=talalka.end())
    {
        cout << it ->first << " "<< it ->second;
        ++it;
    }
    return 0;
}