#include <bits/stdc++.h>
using namespace std;
#define pii pair<int, int>
#define fi first
#define se second

int main()
{
    int n, a, b, state=0, start=0;
    multiset<pii> s;
    vector<pii> op;
    cin >> n >> n;
    while (n--){
        cin >> a >> b;
        s.insert({a, 1});
        s.insert({b, -1});
    }
    cin >> n;
    while (n--){
        cin >> a >> b;
        s.insert({a, 1});
        s.insert({b, -1});
    }
    while (!s.empty()){
        pii p = *s.begin();
        s.erase(s.begin());
        state += p.se;
        if (state == 2){
            start = p.fi;
        }
        else if (start){
            op.push_back({start, p.fi});
            start = 0;
        }
    }
    cout << op.size() << "\n";
    for (pii x : op){
        cout << x.fi << " " << x.se << "\n";
    }
}