#include using namespace std; #define FOR(i,m,n) for(int i=(m);i<(n);++i) #define REP(i,n) FOR(i,0,n) #define ALL(v) (v).begin(),(v).end() using ll = long long; constexpr int INF = 0x3f3f3f3f; constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL; constexpr double EPS = 1e-8; constexpr int MOD = 998244353; // constexpr int MOD = 1000000007; constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1}; constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1}; constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1}; template inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; } template inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; } struct IOSetup { IOSetup() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); std::cout << fixed << setprecision(20); } } iosetup; template struct MInt { unsigned int v; constexpr MInt() : v(0) {} constexpr MInt(const long long x) : v(x >= 0 ? x % M : x % M + M) {} static constexpr MInt raw(const int x) { MInt x_; x_.v = x; return x_; } static constexpr int get_mod() { return M; } static constexpr void set_mod(const int divisor) { assert(std::cmp_equal(divisor, M)); } static void init(const int x) { inv(x); fact(x); fact_inv(x); } template static MInt inv(const int n) { // assert(0 <= n && n < M && std::gcd(n, M) == 1); static std::vector inverse{0, 1}; const int prev = inverse.size(); if (n < prev) return inverse[n]; if constexpr (MEMOIZES) { // "n!" and "M" must be disjoint. inverse.resize(n + 1); for (int i = prev; i <= n; ++i) { inverse[i] = -inverse[M % i] * raw(M / i); } return inverse[n]; } int u = 1, v = 0; for (unsigned int a = n, b = M; b;) { const unsigned int q = a / b; std::swap(a -= q * b, b); std::swap(u -= q * v, v); } return u; } static MInt fact(const int n) { static std::vector factorial{1}; if (const int prev = factorial.size(); n >= prev) { factorial.resize(n + 1); for (int i = prev; i <= n; ++i) { factorial[i] = factorial[i - 1] * i; } } return factorial[n]; } static MInt fact_inv(const int n) { static std::vector f_inv{1}; if (const int prev = f_inv.size(); n >= prev) { f_inv.resize(n + 1); f_inv[n] = inv(fact(n).v); for (int i = n; i > prev; --i) { f_inv[i - 1] = f_inv[i] * i; } } return f_inv[n]; } static MInt nCk(const int n, const int k) { if (n < 0 || n < k || k < 0) [[unlikely]] return MInt(); return fact(n) * (n - k < k ? fact_inv(k) * fact_inv(n - k) : fact_inv(n - k) * fact_inv(k)); } static MInt nPk(const int n, const int k) { return n < 0 || n < k || k < 0 ? MInt() : fact(n) * fact_inv(n - k); } static MInt nHk(const int n, const int k) { return n < 0 || k < 0 ? MInt() : (k == 0 ? 1 : nCk(n + k - 1, k)); } static MInt large_nCk(long long n, const int k) { if (n < 0 || n < k || k < 0) [[unlikely]] return MInt(); inv(k); MInt res = 1; for (int i = 1; i <= k; ++i) { res *= inv(i) * n--; } return res; } constexpr MInt pow(long long exponent) const { MInt res = 1, tmp = *this; for (; exponent > 0; exponent >>= 1) { if (exponent & 1) res *= tmp; tmp *= tmp; } return res; } constexpr MInt& operator+=(const MInt& x) { if ((v += x.v) >= M) v -= M; return *this; } constexpr MInt& operator-=(const MInt& x) { if ((v += M - x.v) >= M) v -= M; return *this; } constexpr MInt& operator*=(const MInt& x) { v = (unsigned long long){v} * x.v % M; return *this; } MInt& operator/=(const MInt& x) { return *this *= inv(x.v); } constexpr auto operator<=>(const MInt& x) const = default; constexpr MInt& operator++() { if (++v == M) [[unlikely]] v = 0; return *this; } constexpr MInt operator++(int) { const MInt res = *this; ++*this; return res; } constexpr MInt& operator--() { v = (v == 0 ? M - 1 : v - 1); return *this; } constexpr MInt operator--(int) { const MInt res = *this; --*this; return res; } constexpr MInt operator+() const { return *this; } constexpr MInt operator-() const { return raw(v ? M - v : 0); } constexpr MInt operator+(const MInt& x) const { return MInt(*this) += x; } constexpr MInt operator-(const MInt& x) const { return MInt(*this) -= x; } constexpr MInt operator*(const MInt& x) const { return MInt(*this) *= x; } MInt operator/(const MInt& x) const { return MInt(*this) /= x; } friend std::ostream& operator<<(std::ostream& os, const MInt& x) { return os << x.v; } friend std::istream& operator>>(std::istream& is, MInt& x) { long long v; is >> v; x = MInt(v); return is; } }; using ModInt = MInt; template struct FenwickTree { explicit FenwickTree(const int n, const Abelian ID = 0) : n(n), ID(ID), data(n, ID) {} void add(int idx, const Abelian val) { for (; idx < n; idx |= idx + 1) { data[idx] += val; } } Abelian sum(int idx) const { Abelian res = ID; for (--idx; idx >= 0; idx = (idx & (idx + 1)) - 1) { res += data[idx]; } return res; } Abelian sum(const int left, const int right) const { return left < right ? sum(right) - sum(left) : ID; } Abelian operator[](const int idx) const { return sum(idx, idx + 1); } int lower_bound(Abelian val) const { if (val <= ID) [[unlikely]] return 0; int res = 0; for (int mask = std::bit_ceil(static_cast(n + 1)) >> 1; mask > 0; mask >>= 1) { const int idx = res + mask - 1; if (idx < n && data[idx] < val) { val -= data[idx]; res += mask; } } return res; } private: const int n; const Abelian ID; std::vector data; }; int main() { int n; cin >> n; vector b(n), c(n); REP(i, n) cin >> b[i] >> c[i]; vector ord(n); iota(ALL(ord), 0); ranges::sort(ord, {}, [&](const int i) -> int { return c[i]; }); vector a(n + 1, 0); ranges::copy(b, next(a.begin())); ranges::sort(a); a.erase(unique(a.begin(), a.end()), a.end()); const int m = a.size(); FenwickTree num(m); FenwickTree r_sum(m), len_sum(m), mus_r(m), mus_nel(m); ModInt ans = 0; for (const int i : ord) { const int index = distance(a.begin(), ranges::lower_bound(a, b[i])); const int always = num.sum(index, m), len = c[i] - b[i] + 1; ans += ModInt::raw(always) / len; ans += r_sum.sum(index) / len - len_sum.sum(index) * (b[i] - 1) / len; ans -= mus_r.sum(index) / len - mus_nel.sum(index) * (b[i] - 1) / len; num.add(index, 1); r_sum.add(index, ModInt::raw(c[i]) / len); len_sum.add(index, ModInt::inv(len)); const int right = distance(a.begin(), ranges::lower_bound(a, c[i])) - 1; mus_r.add(right, ModInt::raw(c[i]) / len); mus_nel.add(right, ModInt::inv(len)); } cout << (-ans + n * (n - 1LL) / 2) * ModInt::fact(n) / 2 << '\n'; return 0; }