#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <atcoder/modint>
using namespace std;
using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
#define rep(i,n) for(int i=0; i<(int)(n); i++)
const i64 INF = 1001001001001001001;

using Modint = atcoder::static_modint<998244353>;



int main(){
    int N; cin >> N;
    vector<pair<int, pair<bool, Modint>>> Dx;
    rep(i,N){
        int b, c; cin >> b >> c;
        Modint p = Modint(c - b + 1).inv();
        Dx.push_back({ b, make_pair(false, p) });
        Dx.push_back({ c+1, make_pair(true, p) });
    }
    sort(Dx.begin(), Dx.end(), [](pair<int, pair<bool, Modint>> a, pair<int, pair<bool, Modint>> b){ return a.first < b.first; });
    int pos = 0;
    Modint p1 = 0;
    Modint p2 = 0;
    Modint p2int = 0;
    for(auto [t, dx] : Dx){
        p2int += p2 * (t - pos);
        pos = t;
        if(dx.first){
            p1 -= dx.second;
            p2 -= dx.second * p1;
        }
        else{
            p2 += dx.second * p1;
            p1 += dx.second;
        }
    }
    Modint f = 1;
    for(int i=1; i<=N; i++) f *= i;
    Modint ans = (Modint(N) * Modint(N-1) / 4 - p2int / 2) * f;
    cout << ans.val() << endl;
    return 0;
}



struct ios_do_not_sync{
    ios_do_not_sync(){
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} ios_do_not_sync_instance;