#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5;
vector<pair<int, int> > A, B;
vector<pair<int, int> > G;
bool vis[maxn];
bool cmp(pair<int, int> a, pair<int, int> b) {
  return abs(a.first - a.second) > abs(b.first - b.second);
}
bool dmp(pair<int, int> a, pair<int, int> b) {
  return abs(a.first - a.second) < abs(b.first - b.second);
}
int main() {
  int n;
  cin >> n;
  for (int i = 1; i <= n - 3; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    if (u == 1 || v == 1) continue;
    if (u > v) swap(u, v);
    A.push_back(make_pair(u, v));
  }
  sort(A.begin(), A.end(), cmp);
  G = A;
  A.clear();
  B = G;
  G.clear();
  for (int i = 1; i <= n - 3; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    if (u == 1 || v == 1) continue;
    if (u > v) swap(u, v);
    A.push_back(make_pair(u, v));
  }
  sort(A.begin(), A.end(), dmp);
  for (auto it : A) {
    int a = it.first, b = it.second;
    for (int i = a + 1; i < b; i++) {
      if (!vis[i]) {
        G.push_back(make_pair(1, i));
        vis[i] = 1;
      }
    }
  }
  cout << G.size() + B.size() << endl;
  for (auto it : B) cout << it.first << " " << it.second << endl;
  for (auto it : G) cout << it.first << " " << it.second << endl;
}
