#include using namespace std; using ll = long long; template struct prime_modint { using mint = prime_modint; unsigned int v; prime_modint() : v(0) {} prime_modint(unsigned int a) { a %= MOD; v = a; } prime_modint(unsigned long long a) { a %= MOD; v = a; } prime_modint(int a) { a %= (int)(MOD); if(a < 0)a += MOD; v = a; } prime_modint(long long a) { a %= (int)(MOD); if(a < 0)a += MOD; v = a; } static constexpr int mod() { return MOD; } mint& operator++() {v++; if(v == MOD)v = 0; return *this;} mint& operator--() {if(v == 0)v = MOD; v--; return *this;} mint operator++(int) { mint result = *this; ++*this; return result; } mint operator--(int) { mint result = *this; --*this; return result; } mint& operator+=(const mint& rhs) { v += rhs.v; if(v >= MOD) v -= MOD; return *this; } mint& operator-=(const mint& rhs) { if(v < rhs.v) v += MOD; v -= rhs.v; return *this; } mint& operator*=(const mint& rhs) { v = (unsigned int)((unsigned long long)(v) * rhs.v % MOD); return *this; } mint& operator/=(const mint& rhs) { return *this = *this * rhs.inv(); } mint operator+() const { return *this; } mint operator-() const { return mint() - *this; } mint pow(long long n) const { assert(0 <= n); mint r = 1, x = *this; while (n) { if (n & 1) r *= x; x *= x; n >>= 1; } return r; } mint inv() const { assert(v); return pow(MOD - 2); } friend mint operator+(const mint& lhs, const mint& rhs) { return mint(lhs) += rhs; } friend mint operator-(const mint& lhs, const mint& rhs) { return mint(lhs) -= rhs; } friend mint operator*(const mint& lhs, const mint& rhs) { return mint(lhs) *= rhs; } friend mint operator/(const mint& lhs, const mint& rhs) { return mint(lhs) /= rhs; } friend bool operator==(const mint& lhs, const mint& rhs) { return (lhs.v == rhs.v); } friend bool operator!=(const mint& lhs, const mint& rhs) { return (lhs.v != rhs.v); } friend std::ostream& operator << (std::ostream &os, const mint& rhs) noexcept { return os << rhs.v; } }; //using mint = prime_modint<1000000007>; using mint = prime_modint<998244353>; template struct lazy_segtree { public: lazy_segtree() : lazy_segtree(0) {} lazy_segtree(int n) : lazy_segtree(std::vector(n, e())) {} lazy_segtree(const std::vector& v) : _n(int(v.size())) { log = ceil_pow2(_n); size = 1 << log; d = std::vector(2 * size, e()); lz = std::vector(size, id()); for (int i = 0; i < _n; i++) d[size + i] = v[i]; for (int i = size - 1; i >= 1; i--) { update(i); } } void set(int p, S x) { assert(0 <= p && p < _n); p += size; for (int i = log; i >= 1; i--) push(p >> i); d[p] = x; for (int i = 1; i <= log; i++) update(p >> i); } S get(int p) { assert(0 <= p && p < _n); p += size; for (int i = log; i >= 1; i--) push(p >> i); return d[p]; } S prod(int l, int r) { assert(0 <= l && l <= r && r <= _n); if (l == r) return e(); l += size; r += size; for (int i = log; i >= 1; i--) { if (((l >> i) << i) != l) push(l >> i); if (((r >> i) << i) != r) push(r >> i); } S sml = e(), smr = e(); while (l < r) { if (l & 1) sml = op(sml, d[l++]); if (r & 1) smr = op(d[--r], smr); l >>= 1; r >>= 1; } return op(sml, smr); } S all_prod() { return d[1]; } void apply(int p, F f) { assert(0 <= p && p < _n); p += size; for (int i = log; i >= 1; i--) push(p >> i); d[p] = mapping(f, d[p]); for (int i = 1; i <= log; i++) update(p >> i); } void apply(int l, int r, F f) { assert(0 <= l && l <= r && r <= _n); if (l == r) return; l += size; r += size; for (int i = log; i >= 1; i--) { if (((l >> i) << i) != l) push(l >> i); if (((r >> i) << i) != r) push((r - 1) >> i); } { int l2 = l, r2 = r; while (l < r) { if (l & 1) all_apply(l++, f); if (r & 1) all_apply(--r, f); l >>= 1; r >>= 1; } l = l2; r = r2; } for (int i = 1; i <= log; i++) { if (((l >> i) << i) != l) update(l >> i); if (((r >> i) << i) != r) update((r - 1) >> i); } } template int max_right(int l) { return max_right(l, [](S x) { return g(x); }); } template int max_right(int l, G g) { assert(0 <= l && l <= _n); assert(g(e())); if (l == _n) return _n; l += size; for (int i = log; i >= 1; i--) push(l >> i); S sm = e(); do { while (l % 2 == 0) l >>= 1; if (!g(op(sm, d[l]))) { while (l < size) { push(l); l = (2 * l); if (g(op(sm, d[l]))) { sm = op(sm, d[l]); l++; } } return l - size; } sm = op(sm, d[l]); l++; } while ((l & -l) != l); return _n; } template int min_left(int r) { return min_left(r, [](S x) { return g(x); }); } template int min_left(int r, G g) { assert(0 <= r && r <= _n); assert(g(e())); if (r == 0) return 0; r += size; for (int i = log; i >= 1; i--) push((r - 1) >> i); S sm = e(); do { r--; while (r > 1 && (r % 2)) r >>= 1; if (!g(op(d[r], sm))) { while (r < size) { push(r); r = (2 * r + 1); if (g(op(d[r], sm))) { sm = op(d[r], sm); r--; } } return r + 1 - size; } sm = op(d[r], sm); } while ((r & -r) != r); return 0; } private: int _n, size, log; std::vector d; std::vector lz; void update(int k) { d[k] = op(d[2 * k], d[2 * k + 1]); } void all_apply(int k, F f) { d[k] = mapping(f, d[k]); if (k < size) lz[k] = composition(f, lz[k]); } void push(int k) { all_apply(2 * k, lz[k]); all_apply(2 * k + 1, lz[k]); lz[k] = id(); } int ceil_pow2(int n) { int x = 0; while ((1U << x) < (unsigned int)(n)) x++; return x; } }; using S = array; using F = array; S op(S lhs, S rhs){ lhs[0] += rhs[0]; lhs[1] += rhs[1]; lhs[2] += rhs[2]; return lhs; } S e(){ S a{}; return a; } S mapping(F f, S x){ x[0] += f[0] * x[1] + f[1] * x[1] - f[2] * x[2]; return x; } F composition(F f, F g){ return F({f[0] + g[0], f[1] + g[1], f[2] + g[2]}); } F id(){return F({0, 0, 0});} int main(){ ios::sync_with_stdio(false); cin.tie(0); int n; cin >> n; vector> a(n), b(n); vector ca(3 * n); vector div(n); for(int i = 0; i < n; i++){ int l, r; cin >> l >> r; a[i] = make_pair(l, r); ca[3 * i] = l; ca[3 * i + 1] = r; ca[3 * i + 2] = r + 1; } sort(ca.begin(), ca.end()); ca.erase(unique(ca.begin(), ca.end()), ca.end()); vector tmp(ca.size()); mint div2 = mint(1) / 2; for(int i = 0; i + 1 < ca.size(); i++){ tmp[i][1] = ca[i + 1] - ca[i]; tmp[i][2] = mint(ca[i + 1]) * (ca[i + 1] - 1) - mint(ca[i]) * (ca[i] - 1); tmp[i][2] *= div2; } lazy_segtree seg(tmp); mint ans; for(int i = 0; i < n; i++){ int l, r; tie(l, r) = a[i]; div[i] = mint(1) / (r - l + 1); l = lower_bound(ca.begin(), ca.end(), l) - ca.begin(); r = lower_bound(ca.begin(), ca.end(), r) - ca.begin(); ans += seg.prod(l, r + 1)[0] * div[i]; seg.apply(l, r, {0, div[i] * a[i].second, div[i]}); seg.apply(0, l, {1, 0, 0}); b[i] = make_pair(l, r); } seg = lazy_segtree(tmp); for(int i = n - 1; i >= 0; i--){ int l, r; tie(l, r) = b[i]; ans += seg.prod(l, r + 1)[0] * div[i]; seg.apply(l, r, {0, div[i] * a[i].second, div[i]}); seg.apply(0, l, {1, 0, 0}); } for(int i = 3; i <= n; i++) ans *= i; cout << ans << '\n'; }