#include<bits/stdc++.h>
#include<atcoder/modint>
using namespace atcoder;
using mint=modint998244353;
using namespace std;
using ll=long long;


int main() {
    ll N;
    cin>>N;
    vector<ll> L(N),R(N);
    mint an=0;
    for(int i=0;i<N;i++){
        cin>>L[i]>>R[i];
        if(i!=0){
            bool rv=0;
            if(R[i]<R[0]){
                rv=1;
                swap(R[i],R[0]);
                swap(L[i],L[0]);
            }
            ll sm=min(R[i],R[0])-max(L[i],L[0])+1;
            sm=max(0ll,sm);
            mint res=0;
            res+=mint(max(0ll,min(L[i],R[0]+1)-L[0]))*(R[i]-L[i]+1);
            ll lf=max(L[i],L[0]);
            ll ri=min(R[i],R[0]);
            if(ri>=lf){
                res+=mint(ri-lf+1)*R[i];
                res-=ri*(ri+1)/2;
                res+=lf*(lf-1)/2;
            }
            
            if(rv){
                swap(R[i],R[0]);
                swap(L[i],L[0]);
                res=mint(R[i]-L[i]+1)*mint(R[0]-L[0]+1)-res-sm;
            }
            an+=res/mint(R[i]-L[i]+1);
        }
    }
    an/=mint(R[0]-L[0]+1);
    an+=1;
    cout<<an.val()<<endl;
}