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

using namespace std;

vector<vector<int> > ki;

int main()
{
    int n,adam,eva,a,b,szamlalo=0;
    cin>>n;
    map<int,int> nums;
    cin>>adam;
    while(adam--)
    {
        cin>>a>>b;
        ++nums[a];
        --nums[b];
    }
    cin>>eva;
    while(eva--)
    {
        cin>>a>>b;
        ++nums[a];
        --nums[b];
    }
    for(int i=1;i<=n;i++)
    {
        /*szamlalo+=nums[i];
        if(szamlalo==2 && nums[i]>0)
        {
            ki.push_back({i});
            continue;
        }
        if((szamlalo==1 && nums[i]==-1) || (szamlalo==0 && nums[i]==-2))
        {
            ki.back().push_back(i);
            continue;
        }*/
    }
    cout<<ki.size()<<"\n";
    for(auto x:ki) cout<<x[0]<<" "<<x[1]<<"\n";
    return 0;
}