#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
using mint = modint998244353;
const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
template<typename T>
std::pair<std::vector<T>, int> compression(std::vector<T>org) {
	auto copy = org;
	std::sort(copy.begin(), copy.end());
	copy.erase(unique(copy.begin(), copy.end()), copy.end());
	for (auto &e : org) {
		e = std::lower_bound(copy.begin(), copy.end(), e) - copy.begin();
	}
	return { org,copy.size() };
}
void invdebug(int x,int y =1) {
	mint m = x;
	m /= y;
	cout << x << "/" << y << "=" << m.val() << endl;
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n; cin >> n;
	vector<int>l(n), r(n);
	rep(i, n) {
		cin >> l[i] >> r[i];
		r[i]++;
	}
	vector<int>c;
	rep(i, n) {
		c.push_back(l[i]);
		c.push_back(r[i]);
	}
	auto compc = compression(c);
	map<int, int>mp, rmp;
	rep(i, c.size())mp[compc.first[i]] = c[i];
	rep(i, c.size())rmp[c[i]] = compc.first[i];
	int sz = compc.second;
	vector<mint>imos(sz), simos(sz + 1);
	rep2(i, 1, n) {
		int x = rmp[l[i]];
		int y = rmp[r[i]];
		mint inv = mint::raw(r[i] - l[i]).inv();
		imos[x] += inv;
		imos[y] -= inv;
	}
	rep(i, sz - 1)imos[i + 1] += imos[i];
	rep(i, sz - 1)imos[i] *= mp[i + 1] - mp[i];
	rep(i, sz + 1)simos[i + 1] += simos[i] + imos[i];

	int st = rmp[l[0]];
	int ed = rmp[r[0]];
	mint ans = 1;
	mint inv = mint::raw(r[0] - l[0]).inv();
	rep2(i, st, ed) {
		{
			mint p = simos[sz] - simos[i + 1];
			mint q = inv * (mp[i + 1] - mp[i]);
			ans += p * q;
		}
		{
			int w = mp[i + 1] - mp[i];
			mint p = simos[i + 1] - simos[i];
			p /= w;
			mint q = inv;
			mint r = mint::raw(w)*(w - 1) / 2;
			//cout << p.val() << endl;
			//cout << q.val() << endl;
			//cout << r.val() << endl;
			ans += p * q * r;
		}

	}
	cout << ans.val() << endl;
	//invdebug(1, 10);
	//invdebug(3, 10);
	//invdebug(45, 1);
	return 0;
}