#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3fffffff;
const int SINF = 0x7fffffff;
const long long LINF = 0x3fffffffffffffff;
const long long SLINF = 0x7fffffffffffffff;
const int MAXN = 1007;
int n;
set<int> ea[MAXN], eb[MAXN];
void init();
void input();
void work();
vector<pair<pair<int, int>, pair<int, int> > > getmd(set<int> e[]);
void getmd(set<int> e[], int l, int r,
           vector<pair<pair<int, int>, pair<int, int> > >& md);
void link(set<int> e[], int u, int v) {
  e[u].insert(v);
  e[v].insert(u);
}
void cut(set<int> e[], int u, int v) {
  e[u].erase(v);
  e[v].erase(u);
}
int main() {
  init();
  input();
  work();
}
void init() { ios::sync_with_stdio(false); }
void input() {
  scanf("%d", &n);
  int u, v;
  for (int i = 0; i < n - 3; ++i) {
    scanf("%d%d", &u, &v);
    ea[u].insert(v);
    ea[v].insert(u);
  }
  for (int i = 0; i < n - 3; ++i) {
    scanf("%d%d", &u, &v);
    eb[u].insert(v);
    eb[v].insert(u);
  }
}
void work() {
  for (int i = 1; i <= n; ++i) link(ea, i, i % n + 1), link(eb, i, i % n + 1);
  vector<pair<pair<int, int>, pair<int, int> > > mda = getmd(ea);
  vector<pair<pair<int, int>, pair<int, int> > > mdb = getmd(eb);
  reverse(mdb.begin(), mdb.end());
  printf("%d\n", mda.size() + mdb.size());
  for (auto x : mda) printf("%d %d\n", x.first.first, x.first.second);
  for (auto x : mdb) printf("%d %d\n", x.second.first, x.second.second);
}
vector<pair<pair<int, int>, pair<int, int> > > getmd(set<int> e[]) {
  vector<pair<pair<int, int>, pair<int, int> > > ans;
  int pre = 2;
  for (auto x : e[1])
    if (x ^ 2) getmd(e, pre, x, ans), pre = x;
  return ans;
}
void getmd(set<int> e[], int l, int r,
           vector<pair<pair<int, int>, pair<int, int> > >& md) {
  if (r - l == 1) return;
  assert(e[l].find(r) != e[l].end());
  for (auto x : e[l]) {
    if ((x > l && x < r) && (e[r].find(x) != e[r].end())) {
      link(e, 1, x);
      cut(e, l, r);
      md.push_back(make_pair(make_pair(l, r), make_pair(1, x)));
      getmd(e, l, x, md);
      getmd(e, x, r, md);
      break;
    }
  }
}
