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




bool vankozospont(pair<int,int> a, pair<int,int> b)
{
    return max(a.first, b.first) < min(a.second, b.second);
}



int main()
{
    int n;
    cin>>n;
    int a,e;
    cin>>a;
    vector<pair<int,int>> adam(a);
    for(int i=0;i<a;i++)
        {
        cin>>adam[i].first>>adam[i].second;
        }

    cin>>e;
    vector<pair<int,int>> eva(e);
    for(int i=0;i<e;i++)
        {
        cin>>eva[i].first>>eva[i].second;
        }
    int evap,adamp;
    evap=adamp=0;
    vector<pair<int,int>>ans;
    while(adamp<a && evap<e)
        {
        if(vankozospont(adam[adamp],eva[evap]))
            {
            ans.push_back({max(adam[adamp].first,eva[evap].first),min(adam[adamp].second,eva[evap].second)});
            if(adam[adamp].second<eva[evap].second)
                {
                adamp++;
                continue;
                }
            else
                {
                evap++;
                continue;
                }
            }
        else
            {
            if(adam[adamp].second<eva[evap].second)
                {
                adamp++;
                continue;
                }
            else
                {
                evap++;
                continue;
                }
            }
        }
    cout<<ans.size()<<endl;
    for(auto x : ans)
        {
        cout<<x.first<<" "<<x.second<<endl;
        }
    return 0;
}