#include <bits/stdc++.h>
#include <atcoder/all>
// url https://yukicoder.me/problems/no/2336
#define rep(i,a,b) for(int i=a;i<b;i++)
#define rrep(i,a,b) for(int i=b-1;i>=a;i--)
#define all(x) (x).begin(),(x).end()
#define pb(x) push_back(x);
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a = b; return 1; } return 0; }
typedef long long ll;
typedef long double lld;
using namespace std;
using namespace atcoder;
using mint = static_modint<998244353>;
const ll mod=998244353;
// using mint = static_modint<1000000007>;
//const ll mod=1e9+7;
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};
const string zton="0123456789";
const string atoz="abcdefghijklmnopqrstuvwxyz";
const string ATOZ="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const ll inf=(1ll<<60);
// const int inf=(1<<30);
lld dist(lld x1,lld x2,lld y1,lld y2){
    lld res=(x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);
    res=sqrt(abs(res));
    return res;
}
lld arg(lld x,lld y){
    const lld eps=1e-8;
    lld res=0;
    if(abs(x)+abs(y)<=eps)return 0.0;
    else if(abs(x)<=eps){
        if(y>=0.0)return (M_PI/2);
        else return (M_PI/2+M_PI);
    }
    else if(abs(y)<=eps){
        if(x>=0.0)return 0.0;
        else return M_PI;
    }
    res=atan2(abs(y),abs(x));
    if(x<=0&&y>=0)res=(M_PI-res);
    else if(x<=0&&y<=0)res+=(M_PI);
    else if(x>=0&&y<=0)res=(M_PI*2-res);
    return res;
}
ll gcd(ll a,ll b){
    if(a==0||b==0)return a+b;
    ll r;
    r=a%b;
    if(r==0){
        return b;
    }
    else{
        return gcd(b,r);
    }
}
typedef pair<ll,int> P;

int N;
vector<ll> B,C;
int main(void){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cin>>N;
    B.resize(N);
    C.resize(N);
    vector<int> v;
    v.pb(0);
    rep(i,0,N){
        cin>>B[i]>>C[i];
        B[i]--;
        v.pb(B[i]);
        v.pb(C[i]);
    }
    sort(all(v));
    v.erase(unique(all(v)),v.end());
    int n=v.size();
    mint imos1[n+1],imos2[n+1];
    rep(i,0,N){
        int l_id=lower_bound(all(v),B[i])-v.begin();
        int r_id=lower_bound(all(v),C[i])-v.begin();
        mint ad=1;
        ad/=(C[i]-B[i]);
        imos1[l_id]+=ad;
        imos1[r_id]-=ad;
        imos2[l_id]+=ad*ad;
        imos2[r_id]-=ad*ad;
    }
    rep(i,0,n){
        imos1[i+1]+=imos1[i];
        imos2[i+1]+=imos2[i];
    }
    mint imos[n+1];
    rep(i,0,n){
        imos[i]=imos1[i]*imos1[i]-imos2[i];
    }
    mint ans=0;
    rep(i,0,n){
        ans+=imos[i]*(v[i+1]-v[i]);
    }
    ans/=2;
    mint ans2=N;
    ans2*=(N-1);
    ans2/=2;
    ans2=ans2-ans;
    rep(i,3,N+1){
        ans2*=i;
    }
    cout<<ans2.val()<<endl;
    // cout << (ans*9).val() << endl;
}