#include<bits/stdc++.h>
#include<atcoder/all>
using namespace std;
using namespace atcoder;

typedef modint998244353 mint;
typedef long long ll;

//defmodfact
const int COMinitMAX = 998244;
mint fact[COMinitMAX+1], factinv[COMinitMAX+1];

void modfact(){
	fact[0] = 1;
	for (int i=1; i<=COMinitMAX; i++){
		fact[i] = fact[i-1] * i;
	}
	factinv[COMinitMAX] = fact[COMinitMAX].inv();
	for (int i=COMinitMAX-1; i>=0; i--){
		factinv[i] = factinv[i+1] * (i+1);
	}
}

mint cmb(int a, int b){
	if (a<b || b<0) return mint(0);
	return fact[a]*factinv[b]*factinv[a-b];
}
//--------

// defcomp
template <typename T>
vector<T> compress(vector<T> &X) {
	vector<T> vals = X;
	sort(vals.begin(), vals.end());
	vals.erase(unique(vals.begin(), vals.end()), vals.end());
	return vals;
}
// -----

// importbisect
template <typename T>
int bisect_left(vector<T> &X, T v){
	return lower_bound(X.begin(), X.end(), v) - X.begin();
}

template <typename T>
int bisect_right(vector<T> &X, T v){
	return upper_bound(X.begin(), X.end(), v) - X.begin();
}
// -----

int main(){
	modfact();
	int n;
	cin >> n;
	vector<int> b(n), c(n);
	vector<int> val;
	for (int i=0; i<n; i++){
		cin >> b[i] >> c[i];
		b[i]--;
		val.push_back(b[i]);
		val.push_back(c[i]);
	}
	vector<int> v = compress(val);
	int m = v.size();
	vector<mint> imos(m + 1);
	for (int i=0; i<n; i++){
		imos[bisect_left(v, b[i])] += mint(1) / mint(c[i] - b[i]);
		imos[bisect_left(v, c[i])] -= mint(1) / mint(c[i] - b[i]);
	}
	for (int i=0; i<m; i++){
		imos[i+1] += imos[i];
	}
	mint nowval = 0;
	mint ret = 0;
	for (int i=0; i<m-1; i++){
		ret += imos[i] * (v[i+1] - v[i]) * (nowval * 2 + imos[i] * (v[i+1] - v[i] - 1)) / 2;
		nowval += imos[i] * (v[i+1] - v[i]);
		//cout << ret.val() << endl;
		//cout << ret.val() << endl;
	}
	for (int i=0; i<n; i++){
		ret -= mint(c[i] - b[i] - 1) / 2 / mint(c[i] - b[i]); 
	}
	//cout << ret.val() << endl;
	ret *= fact[n] / 2;
	cout << ret.val() << endl;
}