#include <bits/stdc++.h>
using namespace std;
bitset<1010> a[1010], b;
int ans1[1010][2], ans2[1010][2];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) a[i][i % n + 1] = a[i % n + 1][i] = 1;
  for (int i = 0; i < n - 3; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    a[x][y] = a[y][x] = 1;
  }
  int m1 = 0, m2 = 0;
  while (1) {
    bool ok = 0;
    for (int i = 3; i < n; i++)
      if (!a[1][i]) {
        int k = i;
        while (!a[1][k]) k++;
        b = a[i - 1] & a[k];
        int x;
        for (int j = 2; j <= n; j++)
          if (b[j]) {
            x = j;
            break;
          }
        ans1[++m1][0] = i - 1;
        ans1[m1][1] = k;
        a[1][x] = a[x][1] = 1;
        a[i - 1][k] = a[k][i - 1] = 0;
        ok = 1;
        break;
      }
    if (!ok) break;
  }
  for (int i = 1; i <= n; i++) a[i].reset();
  for (int i = 1; i <= n; i++) a[i][i % n + 1] = a[i % n + 1][i] = 1;
  for (int i = 0; i < n - 3; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    a[x][y] = a[y][x] = 1;
  }
  while (1) {
    bool ok = 0;
    for (int i = 3; i < n; i++)
      if (!a[1][i]) {
        int k = i;
        while (!a[1][k]) k++;
        b = a[i - 1] & a[k];
        int x;
        for (int j = 2; j <= n; j++)
          if (b[j]) {
            x = j;
            break;
          }
        ans2[++m2][0] = 1;
        ans2[m2][1] = x;
        a[1][x] = a[x][1] = 1;
        a[i - 1][k] = a[k][i - 1] = 0;
        ok = 1;
        break;
      }
    if (!ok) break;
  }
  printf("%d\n", m1 + m2);
  for (int i = 1; i <= m1; i++) printf("%d %d\n", ans1[i][0], ans1[i][1]);
  for (int i = m2; i; i--) printf("%d %d\n", ans2[i][0], ans2[i][1]);
  return 0;
}
