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

using namespace std;

long long int n,m,a,b,szamlalo=0;
vector<vector<long long int> > ki;
map<long long int,long long int> seged;

int main()
{
    cin>>n;
    cin>>m;
    while(m--)
    {
        cin>>a>>b;
        seged[a]++;
        seged[b]--;
    }
    cin>>m;
    while(m--)
    {
        cin>>a>>b;
        seged[a]++;
        seged[b]--;
    }
    for(auto x:seged)
    {
        szamlalo+=x.second;
        if(szamlalo==2 && x.second>0)
        {
            ki.push_back({x.first});
            continue;
        }
        if((szamlalo==1 && x.second==-1) || (szamlalo==0 && x.second==-2))
        {
            ki.back().push_back(x.first);
            continue;
        }
    }
    cout<<ki.size()<<"\n";
    for(auto x:ki) cout<<x[0]<<" "<<x[1]<<"\n";
    return 0;
}