#include <bits/stdc++.h>
using namespace std;
int n, E[1010][1010];
pair<int, int> Sol(int x, int y, int inv) {
  int l = -1, r = 0;
  for (int i = 0; i < n; i++) {
    if (E[x][i] && E[y][i]) {
      if (l == -1)
        l = i;
      else {
        r = i;
        break;
      }
    }
  }
  E[x][y] = E[y][x] = 0;
  E[l][r] = E[r][l] = 1;
  return !inv ? make_pair(x, y) : make_pair(l, r);
}
vector<pair<int, int> > solve(int inv) {
  memset(E, 0, sizeof(E));
  vector<pair<int, int> > res;
  for (int i = 0; i < n; i++) E[i][(i + 1) % n] = E[(i + 1) % n][i] = 1;
  for (int i = 1, l, r; i < n - 2; i++) {
    cin >> l >> r;
    l--, r--;
    E[l][r] = E[r][l] = 1;
  }
  for (int i = 1, j; i < n;) {
    if (E[0][i]) {
      i++;
      continue;
    }
    for (j = i + 1; E[0][j] == 0; j++)
      ;
    res.push_back(Sol(i - 1, j, inv));
  }
  return res;
}
int main() {
  cin >> n;
  vector<pair<int, int> > a = solve(0), b = solve(1);
  cout << a.size() + b.size() << endl;
  for (int i = 0; i < a.size(); i++)
    cout << a[i].first + 1 << " " << a[i].second + 1 << endl;
  for (int i = b.size() - 1; i >= 0; i--)
    cout << b[i].first + 1 << " " << b[i].second + 1 << endl;
  return 0;
}
