#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; }