#if __INCLUDE_LEVEL__ == 0

#include <bits/stdc++.h>

using namespace std;

#undef assert
#define assert(expr) (expr) || (__builtin_unreachable(), 0)

#include __BASE_FILE__

#define ALL(f, r, ...) \
  [&](auto&& _) { return f(begin(_), end(_), ##__VA_ARGS__); }(r)

namespace std::ranges::views {

namespace {

using Fp = atcoder::modint998244353;

void solve() {
  int n;
  cin >> n;
  vector<int> b(n), c(n);
  for (int i : iota(0, n)) {
    cin >> tie(b[i], c[i]);
    ++c[i];
  }
  auto U = b;
  U.insert(U.end(), c.begin(), c.end());
  sort(U);
  ALL(U.erase, unique(U));
  auto rank = [&](int x) { return lower_bound(U, x) - U.begin(); };
  vector<Fp> f(U.size());
  vector<Fp> f2(U.size());
  for (int i : iota(0, n)) {
    int l = rank(b[i]);
    int r = rank(c[i]);
    Fp t = 1 / Fp(c[i] - b[i]);
    f[l] += t;
    f[r] -= t;
    f2[l] += t * t;
    f2[r] -= t * t;
  }
  ALL(partial_sum, f, f.begin());
  ALL(partial_sum, f2, f2.begin());
  Fp ans = 0;
  for (int i : iota(1, ssize(U))) {
    Fp w = U[i] - U[i - 1];
    Fp cur = (f[i - 1] * f[i - 1] - f2[i - 1]) / 2;
    ans += cur * w;
  }
  ans = n * Fp(n - 1) / 2 - ans;
  for (int i : iota(0, n)) {
    ans *= i + 1;
  }
  ans /= 2;
  cout << ans << '\n';
}

}  // namespace

}  // namespace std::ranges::views

using views::solve;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  solve();
}

#else  // __INCLUDE_LEVEL__

#include <atcoder/modint>

namespace std {

template <class T1, class T2>
istream& operator>>(istream& is, pair<T1, T2>& p) {
  return is >> p.first >> p.second;
}

template <class... Ts>
istream& operator>>(istream& is, tuple<Ts...>& t) {
  return apply([&is](auto&... xs) -> istream& { return (is >> ... >> xs); }, t);
}

template <class... Ts>
istream& operator>>(istream& is, tuple<Ts&...>&& t) {
  return is >> t;
}

template <class R, enable_if_t<!is_convertible_v<R, string>>* = nullptr>
auto operator>>(istream& is, R&& r) -> decltype(is >> *begin(r)) {
  for (auto&& e : r) {
    is >> e;
  }
  return is;
}

template <class T1, class T2>
ostream& operator<<(ostream& os, const pair<T1, T2>& p) {
  return os << p.first << ' ' << p.second;
}

template <class... Ts>
ostream& operator<<(ostream& os, const tuple<Ts...>& t) {
  auto f = [&os](const auto&... xs) -> ostream& {
    [[maybe_unused]] auto sep = "";
    ((os << exchange(sep, " ") << xs), ...);
    return os;
  };
  return apply(f, t);
}

template <class R, enable_if_t<!is_convertible_v<R, string_view>>* = nullptr>
auto operator<<(ostream& os, R&& r) -> decltype(os << *begin(r)) {
  auto sep = "";
  for (auto&& e : r) {
    os << exchange(sep, " ") << e;
  }
  return os;
}

}  // namespace std

namespace atcoder {

template <class T, internal::is_modint_t<T>* = nullptr>
istream& operator>>(istream& is, T& x) {
  int v;
  is >> v;
  x = T::raw(v);
  return is;
}

template <class T, internal::is_modint_t<T>* = nullptr>
ostream& operator<<(ostream& os, const T& x) {
  return os << x.val();
}

}  // namespace atcoder

#endif  // __INCLUDE_LEVEL__