#include <bits/stdc++.h>
using namespace std;
void in(vector<vector<int> >& v) {
  int n = v.size();
  for (int i = 0; i + 3 < v.size(); ++i) {
    int a, b;
    cin >> a >> b;
    --a;
    --b;
    v[a][b] = 1;
    v[b][a] = 1;
  }
  for (int i = 0; i < n; ++i) {
    v[i][(i + 1) % n] = 1;
    v[(i + 1) % n][i] = 1;
  }
}
vector<vector<int> > f(vector<vector<int> > v) {
  vector<vector<int> > res;
  vector<int> x(4);
  int n = v.size();
  for (int i = 2; i < n - 1; ++i)
    if (!v[0][i]) {
      assert(v[i - 1][0] == 1);
      for (int j = i + 1; j < n; ++j)
        if (v[0][j]) {
          assert(v[i - 1][j] == 1);
          for (int l = i; l < j; ++l)
            if (v[l][j]) {
              assert(v[0][l] == 0);
              assert(v[i - 1][l] == 1);
              v[i - 1][j] = v[j][i - 1] = 0;
              v[0][l] = v[l][0] = 1;
              x[0] = i - 1;
              x[1] = j;
              x[2] = 0;
              x[3] = l;
              res.push_back(x);
              break;
            }
          break;
        }
      --i;
    }
  return res;
}
int main() {
  int n;
  cin >> n;
  vector<vector<int> > v1(n, vector<int>(n)), v2(n, vector<int>(n));
  in(v1);
  in(v2);
  vector<vector<int> > a = f(v1);
  vector<vector<int> > b = f(v2);
  cout << a.size() + b.size() << endl;
  for (int i = 0; i < a.size(); ++i)
    cout << a[i][0] + 1 << ' ' << a[i][1] + 1 << endl;
  reverse(b.begin(), b.end());
  for (int i = 0; i < b.size(); ++i)
    cout << b[i][2] + 1 << ' ' << b[i][3] + 1 << endl;
  return 0;
}
