#include <iostream>
#include <vector>

using namespace std;

struct adat
{
    int kezd, veg;
};

int i, j, eva, adam, n;
vector <pair <int, int>> idopont;

int main()
{
    cin>>n;

    cin>>eva;
    vector <adat> e(eva+1);
    for (i=1; i<=eva; ++i)
    {
        cin>>e[i].kezd>>e[i].veg;
    }

    cin>>adam;
    vector <adat> a(adam+1);
    for(i=1; i<=adam; ++i)
    {
        cin>>a[i].kezd>>a[i].veg;
    }

    i=1;
    j=1;
    while (i<=eva && j<=adam)
    {
        if (e[i].veg<=a[j].kezd) ++i;
        else if (a[j].veg<=e[i].kezd) ++j;
        else if (e[i].kezd<=a[j].kezd)
        {
            if (e[i].veg>=a[j].veg)
            {
                idopont.push_back({a[j].kezd, a[j].veg});
                ++j;
            }else
            {
                idopont.push_back({a[j].kezd, e[i].veg});
                ++i;
            }
        }else
        {
            if (e[i].veg<=a[j].veg)
            {
                idopont.push_back({e[i].kezd, e[i].veg});
                ++i;
            }else
            {
                idopont.push_back({e[i].kezd, a[j].veg});
                ++j;
            }
        }
    }

    cout<<idopont.size()<<"\n";
    for (auto &e:idopont)
    {
        cout<<e.first<<" "<<e.second<<"\n";
    }

    return 0;
}