#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 1000000000000000001

int main(){
	int N;
	cin>>N;
	int L,R;
	cin>>L>>R;
	mint ans = 1;
	rep(i,N-1){
		int l,r;
		cin>>l>>r;
		if(l>R)continue;//ans++;
		else if(L>r)continue;
		else{
			int sl = max(L,l), sr = min(R,r);
			mint pp = (R-L+1);
			pp *= (r-l+1);
			{
				mint n =sr-sl+1;
				mint cnt = n * (n-1)/2;
				
				ans += cnt / pp;
			}
			if(L<sl){
				mint p = R-L+1;
				ans += mint(sl-L) / p;
			}
			if(r>sr){
				mint p = r-l+1;
				ans += mint(r-sr) / p;
			}
			
		}
	}
	cout<<ans.val()<<endl;
	
    return 0;
}