#include <bits/stdc++.h>
using namespace std;
long long mul(long long a, long long b) {
  return ((a % 998244353) * (b % 998244353)) % 998244353;
}
long long add(long long a, long long b) {
  return ((a % 998244353) + (b % 998244353)) % 998244353;
}
long long sub(long long a, long long b) {
  return ((a % 998244353) - (b % 998244353)) % 998244353;
}
long long fac(long long x) {
  long long resp = 1;
  for (long long i = 1; i <= x; i++) resp = mul(resp, i);
  return resp;
}
bool cmp(pair<int, int> p1, pair<int, int> p2) {
  if (p1.first < p2.first)
    return 1;
  else if (p1.first > p2.first)
    return 0;
  else
    return p1.second < p2.second;
}
bool cmp1(pair<int, int> p1, pair<int, int> p2) {
  return p1.second < p2.second;
}
pair<int, int> arr[300010];
int main() {
  ios_base::sync_with_stdio(false);
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> arr[i].first >> arr[i].second;
  }
  long long ans = fac(n);
  sort(arr, arr + n);
  long long qtd = 1;
  long long c1 = 1;
  for (int i = 1; i < n; i++) {
    if (arr[i].first == arr[i - 1].first)
      qtd++;
    else {
      c1 = mul(c1, fac(qtd));
      qtd = 1;
    }
  }
  c1 = mul(c1, fac(qtd));
  sort(arr, arr + n, cmp1);
  qtd = 1;
  long long c2 = 1;
  for (int i = 1; i < n; i++) {
    if (arr[i].second == arr[i - 1].second)
      qtd++;
    else {
      c2 = mul(c2, fac(qtd));
      qtd = 1;
    }
  }
  c2 = mul(c2, fac(qtd));
  sort(arr, arr + n, cmp);
  bool sorted = true;
  long long cnt12 = 1;
  qtd = 1;
  for (int i = 1; i < n; i++) {
    if (arr[i].second < arr[i - 1].second) sorted = false;
    if (arr[i] == arr[i - 1])
      qtd++;
    else {
      cnt12 = mul(cnt12, fac(qtd));
      qtd = 1;
    }
  }
  cnt12 = mul(cnt12, fac(qtd));
  if (!sorted) cnt12 = 0;
  ans = sub(ans, c1);
  ans = add(ans, cnt12);
  ans = sub(ans, c2);
  cout << (ans + 998244353) % 998244353 << endl;
}
