#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

int main()
{
    int n,a,e,x,y,db=0;
    cin>>n>>a;
    vector<int>h(n-1,0),kp,vp;
    kp.push_back(0);vp.push_back(0);
    for(int i=1; i<=a; i++)
    {
        cin>>x>>y;
        while(x<y){h[x]++; x++;}
    }
    cin>>e;
    for(int i=1; i<=e; i++)
    {
        cin>>x>>y;
        while(x<y){h[x]++; x++;}
    }
    for(int i=1; i<=n-1; i++)
    {
        if(h[i-1]<2 && h[i]==2)
        {
            db++;
            kp.push_back(i);
        }
        if(h[i-1]==2 && h[i]<2)vp.push_back(i);
    }
    cout<<db<<endl;
    for(int i=1; i<=db; i++)
    {
        cout<<kp[i]<<" "<<vp[i]<<endl;
    }
    return 0;
}