#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001

int main(){
	
	int n;
	cin>>n;
	
	vector<int> b(n),c(n);
	vector<int> t;
	rep(i,n){
		cin>>b[i]>>c[i];
		t.push_back(b[i]);
		t.push_back(c[i]+1);
	}
	sort(t.begin(),t.end());
	t.erase(unique(t.begin(),t.end()),t.end());
	vector<vector<int>> Ad(t.size()),De(t.size());
	rep(i,n){
		int d = distance(t.begin(),lower_bound(t.begin(),t.end(),b[i]));
		Ad[d].push_back(i);
		d = distance(t.begin(),lower_bound(t.begin(),t.end(),c[i]+1));
		De[d].push_back(i);
	}
	mint s1 = 0,s2 = 0;
	mint ans = 0;
	
	rep(i,t.size()-1){
		rep(j,Ad[i].size()){
			int ii = Ad[i][j];
			mint p = mint(c[ii]-b[ii]+1).inv();
			s2 += s1 * p;
			s1 += p;
		}
		rep(j,De[i].size()){
			int ii = De[i][j];
			mint p = mint(c[ii]-b[ii]+1).inv();
			s1 -= p;
			s2 -= s1 * p;
		}
		ans += s2 * (t[i+1] - t[i]);
	}
	mint tt = n;
	tt *= n-1;
	tt /= 2;
	ans = tt - ans;
	ans /= 2;
	rep(i,n)ans *= i+1;
	cout<<ans.val()<<endl;
	
	return 0;
}