#include <bits/stdc++.h>
using namespace std;
int main() {
  vector<pair<int, int> > ans[2];
  int n;
  cin >> n;
  vector<int> v[n];
  for (int i = 0; i < n - 3; ++i) {
    int x, y;
    cin >> x >> y;
    if (x != 1 && y != 1) ans[0].emplace_back(min(x, y), -max(x, y));
  }
  sort(ans[0].begin(), ans[0].end());
  for (int i = 0; i < n - 3; ++i) {
    int x, y;
    cin >> x >> y;
    v[min(x, y) - 1].push_back(-max(x, y));
  }
  for (int i = 1; i < n; ++i) {
    sort(v[i].begin(), v[i].end());
    for (int j = 1; j < v[i].size(); ++j) ans[1].emplace_back(1, v[i][j]);
    if (v[i].size()) ans[1].emplace_back(1, -i - 2);
  }
  ans[0].insert(ans[0].end(), ans[1].rbegin(), ans[1].rend());
  cout << ans[0].size() << '\n';
  for (pair<int, int> i : ans[0]) cout << i.first << ' ' << -i.second << '\n';
}
