#include <bits/stdc++.h>
using namespace std;
int INF = INT_MAX;
long long mod = 998244353;
long long power(long long a, long long b) {
  long long result = 1;
  while (b > 0) {
    if (b % 2 == 1) result = (result * a) % mod;
    a = (a * a) % mod;
    b /= 2;
  }
  return result;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  vector<pair<pair<int, int>, int>> a(n);
  for (int i = 0; i < n; i++) {
    cin >> a[i].first.first >> a[i].first.second;
    a[i].second = i;
  }
  sort(a.rbegin(), a.rend());
  vector<pair<int, int>> first(n);
  vector<pair<int, int>> second(n);
  int f;
  int l, r;
  r = 0;
  while (r < n) {
    f = a[r].first.first;
    l = r;
    while (r < n && a[r].first.first == f) {
      r++;
    }
    for (int i = l; i < r; i++) {
      first[a[i].second] = {l, r - 1};
    }
  }
  for (int i = 0; i < n; i++) swap(a[i].first.first, a[i].first.second);
  sort(a.rbegin(), a.rend());
  r = 0;
  while (r < n) {
    f = a[r].first.first;
    l = r;
    while (r < n && a[r].first.first == f) {
      r++;
    }
    for (int i = l; i < r; i++) {
      second[a[i].second] = {l, r - 1};
    }
  }
  long long by_first = 0;
  vector<long long> fact(n + 1);
  fact[0] = 1;
  fact[1] = 1;
  for (int i = 2; i <= n; i++) {
    fact[i] = (fact[i - 1] * i) % mod;
  }
  set<pair<int, int>> dif;
  for (int i = 0; i < n; i++) dif.insert(first[i]);
  set<pair<int, int>>::iterator it;
  it = dif.begin();
  by_first = 1;
  while (it != dif.end()) {
    by_first = (by_first * fact[(*it).second - (*it).first + 1]) % mod;
    it++;
  }
  long long by_second = 1;
  dif.clear();
  for (int i = 0; i < n; i++) dif.insert(second[i]);
  it = dif.begin();
  while (it != dif.end()) {
    by_second = (by_second * fact[(*it).second - (*it).first + 1]) % mod;
    it++;
  }
  bool have = true;
  for (int i = 0; i < n; i++) {
    first[i] = {max(first[i].first, second[i].first),
                min(second[i].second, first[i].second)};
    if (first[i].first > first[i].second) have = false;
  }
  long long intersect = 0;
  if (have) {
    intersect = 1;
    dif.clear();
    for (int i = 0; i < n; i++) dif.insert(first[i]);
    it = dif.begin();
    while (it != dif.end()) {
      intersect = (intersect * fact[(*it).second - (*it).first + 1]) % mod;
      it++;
    }
  }
  long long ans = (by_first + by_second - intersect + mod) % mod;
  ans = (fact[n] - ans + mod) % mod;
  cout << ans << "\n";
}
