#include <bits/stdc++.h>
using namespace std;
const long long MOD = 998244353;
const long long HALF = 499122177;
long long modpow(long long a, long long b){
  long long ans = 1;
  while (b > 0){
    if (b % 2 == 1){
      ans *= a;
      ans %= MOD;
    }
    a *= a;
    a %= MOD;
    b /= 2;
  }
  return ans;
}
long long modinv(long long a){
  return modpow(a, MOD - 2);
}
int main(){
  int N;
  cin >> N;
  vector<int> B(N), C(N);
  for (int i = 0; i < N; i++){
    cin >> B[i] >> C[i];
    C[i]++;
  }
  vector<long long> W(N);
  for (int i = 0; i < N; i++){
    W[i] = modinv(C[i] - B[i]);
  }
  vector<tuple<int, int, int>> X;
  for (int i = 0; i < N; i++){
    X.push_back(make_tuple(B[i], i, 0));
    X.push_back(make_tuple(C[i], i, 1));
  }
  sort(X.begin(), X.end());
  long long ans = (long long) N * (N - 1) / 2 % MOD * HALF % MOD;
  long long sum = 0, sum2 = 0;
  for (int i = 0; i < N * 2; i++){
    int p = get<1>(X[i]);
    int t = get<2>(X[i]);
    if (t == 0){
      sum2 += sum * W[p] % MOD;
      sum2 %= MOD;
      sum += W[p];
      sum %= MOD;
    }
    if (t == 1){
      sum += MOD - W[p];
      sum %= MOD;
      sum2 += MOD - sum * W[p] % MOD;
      sum2 %= MOD;
    }
    if (i < N * 2 - 1){
      ans += MOD - (get<0>(X[i + 1]) - get<0>(X[i])) * sum2 % MOD * HALF % MOD;
      ans %= MOD;
    }
  }
  for (int i = 1; i <= N; i++){
    ans *= i;
    ans %= MOD;
  }
  cout << ans << endl;
}