#include <bits/stdc++.h>
using namespace std;
const int N = 2145;
int n;
struct ask {
  int st, px[N], py[N], a[N][N];
  void dfs(int l, int r) {
    for (int i = l + 1; i <= r; i++)
      if (a[1][i]) {
        for (int k = l + 1; k < i; k++)
          if (a[k][l] && a[k][i]) {
            px[++st] = l, py[st] = i;
            px[++st] = 1;
            py[st] = k;
            a[i][l] = a[l][i] = 0, a[1][k] = a[k][1] = 1;
            dfs(l, k);
            dfs(k, i);
            break;
          }
        l = i;
      }
  }
  void sol() {
    for (int i = 1, x, y; i <= n - 3; i++)
      scanf("%d%d", &x, &y), a[x][y] = a[y][x] = 1;
    for (int i = 1; i <= n; i++) a[i][i % n + 1] = a[i % n + 1][i] = 1;
    dfs(2, n);
  }
} a, b;
int main() {
  scanf("%d", &n);
  a.sol();
  b.sol();
  printf("%d\n", (a.st + b.st) >> 1);
  for (int i = 1; i <= a.st; i += 2) printf("%d %d\n", a.px[i], a.py[i]);
  for (int i = b.st; i; i -= 2) printf("%d %d\n", b.px[i], b.py[i]);
}
