#include <bits/stdc++.h>
using namespace std;
const int N = 3e5 + 10;
const int mod = 998244353;
const int inf = 0x3f3f3f3f;
int fac[N], n;
struct node {
  int a, b;
} g[N];
bool cmp1(const node &o1, const node &o2) { return o1.a < o2.a; }
bool cmp2(const node &o1, const node &o2) { return o1.b < o2.b; }
bool cmp3(const node &o1, const node &o2) {
  if (o1.a == o2.a) return o1.b < o2.b;
  return o1.a < o2.a;
}
int add(int v) { return (v % mod + mod) % mod; }
bool check() {
  for (int i = 2; i <= n; i++) {
    if (g[i].a < g[i - 1].a || g[i].b < g[i - 1].b) return false;
  }
  return true;
}
int main() {
  scanf("%d", &n);
  fac[0] = 1;
  for (int i = 1; i <= n; i++) {
    fac[i] = fac[i - 1] * 1LL * i % mod;
    scanf("%d%d", &g[i].a, &g[i].b);
  }
  sort(g + 1, g + n + 1, cmp1);
  int inv = 1;
  int p = 1;
  while (p <= n) {
    int v = g[p].a, cnt = 0;
    while (p <= n && g[p].a == v) cnt++, p++;
    inv = inv * 1LL * fac[cnt] % mod;
  }
  sort(g + 1, g + n + 1, cmp2);
  p = 1;
  int inv2 = 1;
  while (p <= n) {
    int v = g[p].b, cnt = 0;
    while (p <= n && g[p].b == v) cnt++, p++;
    inv2 = inv2 * 1LL * fac[cnt] % mod;
  }
  int inv3 = 0;
  sort(g + 1, g + n + 1, cmp3);
  if (check()) {
    inv3 = 1;
    p = 1;
    while (p <= n) {
      int v1 = g[p].a, v2 = g[p].b, cnt = 0;
      while (p <= n && g[p].a == v1 && g[p].b == v2) cnt++, p++;
      inv3 = inv3 * 1LL * fac[cnt] % mod;
    }
  }
  inv = (inv + inv2) % mod;
  inv = ((inv - inv3) % mod + mod) % mod;
  inv = ((fac[n] - inv) % mod + mod) % mod;
  printf("%d\n", inv);
  return 0;
}
