#include <bits/stdc++.h>
using namespace std;
template <class T>
inline void rd(T &x) {
  char ch;
  x = 0;
  bool fl = false;
  while (!isdigit(ch = getchar())) (ch == '-') && (fl = true);
  for (x = (ch ^ '0'); isdigit(ch = getchar()); x = x * 10 + (ch ^ '0'))
    ;
  (fl == true) && (x = -x);
}
template <class T>
inline void output(T x) {
  if (x / 10) output(x / 10);
  putchar(x % 10 + '0');
}
template <class T>
inline void ot(T x) {
  if (x < 0) putchar('-'), x = -x;
  output(x);
  putchar(' ');
}
template <class T>
inline void prt(T a[], int st, int nd) {
  for (int i = st; i <= nd; ++i) ot(a[i]);
  putchar('\n');
}
namespace Modulo {
const int mod = 998244353;
inline int ad(int x, int y) { return x + y >= mod ? x + y - mod : x + y; }
inline int sub(int x, int y) { return ad(x, mod - y); }
inline int mul(int x, int y) { return (long long)x * y % mod; }
inline void inc(int &x, int y) { x = ad(x, y); }
inline void inc2(int &x, int y) { x = mul(x, y); }
inline int qm(int x, int y = mod - 2) {
  int ret = 1;
  while (y) {
    if (y & 1) ret = mul(x, ret);
    x = mul(x, x);
    y >>= 1;
  }
  return ret;
}
template <class... Args>
inline int ad(const int a, const int b, const Args &...args) {
  return ad(ad(a, b), args...);
}
template <class... Args>
inline int mul(const int a, const int b, const Args &...args) {
  return mul(mul(a, b), args...);
}
}  // namespace Modulo
using namespace std;
pair<int, int> p[300007];
const long long mod = 998244353LL;
long long fac[300007];
class Task {
 public:
  void solve(istream &in, ostream &out) {
    fac[0] = 1;
    for (long long i = 1; i != 300005; i++) fac[i] = fac[i - 1] * i % mod;
    int n;
    in >> n;
    for (int i = 0; i != n; i++) in >> p[i].first >> p[i].second;
    sort(p, p + n);
    long long ans = fac[n], now = 0, ts = 1, num = 0;
    for (int i = 0; i != n; i++) {
      if (p[i].first != now)
        (ts *= fac[num]) %= mod, num = 1, now = p[i].first;
      else
        num++;
    }
    (ts *= fac[num]) %= mod, ans -= ts;
    bool c = true;
    for (int i = 0; i != n - 1 && c; i++) {
      if (p[i].first > p[i + 1].first || p[i].second > p[i + 1].second) {
        c = false;
      }
    }
    if (c) {
      ts = 1, num = 0;
      for (int i = 0; i != n; i++) {
        if (i == 0 || p[i] != p[i - 1])
          (ts *= fac[num]) %= mod, num = 1;
        else
          num++;
      }
      (ts *= fac[num]) %= mod, ans += ts, num = 1;
    }
    sort(p, p + n, [&](pair<int, int> &p1, pair<int, int> &p2) {
      return p1.second < p2.second;
    });
    now = 0, ts = 1, num = 0;
    for (int i = 0; i != n; i++) {
      if (p[i].second != now)
        (ts *= fac[num]) %= mod, num = 1, now = p[i].second;
      else
        num++;
    }
    (ts *= fac[num]) %= mod, ans -= ts;
    out << (mod + ans % mod) % mod;
  }
};
int main() {
  ios::sync_with_stdio(false);
  Task solver;
  std::istream &in(std::cin);
  std::ostream &out(std::cout);
  solver.solve(in, out);
  return 0;
}
