#include <iostream>
#include <vector>

using namespace std;
struct ember
{
    int k, v;
};

int main()
{
    int p, nA, nE;
    cin >> p;
    cin >> nA;
    vector <ember> a(nA);
    for (int i=0;i<nA;i++)
    {
        cin >> a[i].k >> a[i].v;
    }
    cin >> nE;
    vector <ember> e(nE);
    for (int i=0;i<nE;i++)
    {
        cin >> e[i].k >> e[i].v;
    }
    int i=0, j=0;
    int kez, veg, db=0;
    vector<ember> kozos(p);
    while (i<nA && j<nE)
    {
            kez = max(a[i].k , e[j].k);
            veg = min (a[i].v , e[j].v);
            if (kez<veg)
            {
                kozos[db].k=kez;
                kozos[db].v=veg;
                db++;
            }
            if (e[j].v>a[i].v)
            {
                i++;
            }
            else
            {
                j++;
            }

    }
    cout<<db<<endl;
    for (int i=0;i<db;i++)
    {
        cout << kozos[i].k << " " << kozos[i].v << endl;
    }
    return 0;
}