#include <iostream>
#include <algorithm>
#include <vector>
#include <fstream>
#include <map>

using namespace std;
//ifstream fin("input.in");

int main()
{
    int P, A, E;
    cin >> P;
    cin >> A;
    map<int, int> seged;

    for(int i = 0; i < A; i++){
        int a, b;
        cin >> a >> b;
        seged[a]++;
        seged[b]--;
    }

    cin >> E;
    for(int i = 0; i < E; i++){
        int a, b;
        cin >> a >> b;
        seged[a]++;
        seged[b]--;
    }
    int szabad_szama = 0;
    vector<pair<int, int>> megoldas;
    for(auto x:seged){
        szabad_szama += x.second;
        if(szabad_szama == 2 && x.second > 0){
            megoldas.push_back({x.first, 0});
        }
        if(szabad_szama == 1 && x.second == -1 || szabad_szama == 0 && x.second == -2){
            megoldas.back().second = x.first;
        }
    }
    cout << megoldas.size() << endl;
    for(int i = 0; i < megoldas.size(); i++){
        cout << megoldas[i].first << " " << megoldas[i].second << endl;
    }

    return 0;
}