#include <bits/stdc++.h>
using namespace std;
long long z = 998244353;
long long gcd(long long a, long long b) {
  if (a == 0) return b;
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long power(long long a, long long b) {
  long long res = 1;
  while (b) {
    if (b & 1) {
      res = (res * a) % z;
      b--;
    } else {
      a = (a * a) % z;
      b = b >> 1;
    }
  }
  return res;
}
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long fact[300001];
  fact[0] = 1;
  for (long long i = 1; i <= 300000; i++) {
    fact[i] = i * fact[i - 1];
    fact[i] %= z;
  }
  long long t;
  t = 1;
  while (t--) {
    long long n;
    cin >> n;
    long long a, b;
    vector<pair<long long, long long> > v1, v2;
    for (long long i = 0; i < n; i++) {
      cin >> a >> b;
      v1.push_back(make_pair(a, b));
      v2.push_back(make_pair(b, a));
    }
    sort(v1.begin(), v1.end());
    sort(v2.begin(), v2.end());
    vector<long long> v3, v4;
    long long len = 1;
    for (long long i = 1; i < n; i++) {
      if (v1[i].first == v1[i - 1].first)
        len++;
      else {
        v3.push_back(len);
        len = 1;
      }
    }
    v3.push_back(len);
    len = 1;
    for (long long i = 1; i < n; i++) {
      if (v2[i].first == v2[i - 1].first)
        len++;
      else {
        v4.push_back(len);
        len = 1;
      }
    }
    v4.push_back(len);
    long long ans = fact[n], p = 1, q = 1;
    for (long long i = 0; i < v3.size(); i++) {
      p *= fact[v3[i]];
      p %= z;
      if (i > 0) v3[i] += v3[i - 1];
    }
    for (long long i = 0; i < v4.size(); i++) {
      q *= fact[v4[i]];
      q %= z;
      if (i > 0) v4[i] += v4[i - 1];
    }
    p += q;
    p %= z;
    q = 1;
    len = 1;
    long long c = 0;
    for (long long i = 1; i < n; i++) {
      if (v1[i].first == v1[i - 1].first && v1[i].second == v1[i - 1].second)
        len++;
      else {
        if (v1[i].second < v1[i - 1].second) {
          c++;
          break;
        } else {
          q *= fact[len];
          q %= z;
          len = 1;
        }
      }
    }
    q *= fact[len];
    q %= z;
    if (!c) {
      p -= q;
      if (p < 0) p += z;
    }
    ans -= p;
    if (ans < 0) ans += z;
    cout << ans << "\n";
  }
}
