#include <bits/stdc++.h>
using namespace std;
template <class _Tp>
void ckmax(_Tp &a, _Tp b) {
  if (a < b) a = b;
}
template <class _Tp>
void ckmin(_Tp &a, _Tp b) {
  if (a > b) a = b;
}
template <class _Tp>
_Tp gcd(_Tp a, _Tp b) {
  return (b == 0) ? (a) : (gcd(b, a % b));
}
int read() {
  char ch = getchar();
  bool f = 1;
  int x = 0;
  while ((ch < '0' || ch > '9') && ch != '-') ch = getchar();
  if (ch == '-') f = 0, ch = getchar();
  while (ch >= '0' && ch <= '9') {
    x = x * 10 + (ch & 15);
    ch = getchar();
  }
  return f ? x : -x;
}
const int inf = 1000000000;
const long long Inf = 1000000000000000000ll;
bool a[1050][1050], b[1050][1050];
int n, Q, S, qx[1050], qy[1050], ans[1050];
int main() {
  n = read();
  for (int i = 1, x, y; i <= n - 3; ++i) {
    x = read();
    y = read();
    a[x][y] = a[y][x] = 1;
  }
  for (int i = 1, x, y; i <= n - 3; ++i) {
    x = read();
    y = read();
    b[x][y] = b[y][x] = 1;
  }
  for (int i = 2; i <= n; ++i)
    for (int j = n; j >= i + 2; --j)
      if (a[i][j]) {
        qx[++Q] = i;
        qy[Q] = j;
        a[i][j] = a[j][i] = 0;
      }
  for (int i = 2; i <= n; ++i)
    for (int j = n; j >= i + 2; --j)
      if (b[i][j]) {
        int k;
        for (k = j - 1; k > i; --k)
          if (b[i][k] || k == i + 1) break;
        ans[++S] = k;
        b[i][j] = b[j][i] = 0;
        b[1][ans[S]] = b[ans[S]][1] = 1;
      }
  printf("%d\n", Q + S);
  for (int i = 1; i <= Q; ++i) printf("%d %d\n", qx[i], qy[i]);
  for (int i = S; i >= 1; --i) printf("1 %d\n", ans[i]);
  return 0;
}
