#include<bits/stdc++.h>
#include<atcoder/modint>
using namespace std;
using mint=atcoder::modint998244353;
mint f(mint l, mint r){return (r-l)*(r-l-1)/2;}
int N,L[2<<17],R[2<<17];
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cin>>N;
    for(int i=0;i<N;i++)cin>>L[i]>>R[i],L[i]--;
    mint ans=1;
    for(int i=1;i<N;i++)
    {
        mint sum=0;
        if(L[0]>=R[i])continue;
        if(R[0]<L[i])
        {
            ans++;
            continue;
        }
        if(L[0]<L[i])sum+=(R[i]-L[i])*(L[i]-L[0]);
        if(R[0]<R[i])sum+=(R[0]-L[0])*(R[i]-R[0]);
        sum+=f(max(L[0],L[i]),min(R[0],R[i]));
        sum/=(R[i]-L[i]);
        sum/=(R[0]-L[0]);
        ans+=sum;
    }
    cout<<ans.val()<<endl;
}